Fix Qt designer crash when dropping spinbox in ctkCollapsibleGroupBox

ctkCollapsibleGroupBox (and ctkCollapsibleButton) were setting the visibility
of the newly added child spinbox to ON (at backtrace line 5).
As a side effect, QAbstractSpinBox::setLineEdit() was calling updateEdit()
which was trying to access some RTTI information that is not yet available
(because it was still in the spinbox constructor).

See below the backtrace:
#0  0x00007ffff6d78d50 in typeinfo for QAbstractSpinBox () from /home/julien/work/qt/qt-4.8.5/lib/libQtGui.so.4
#1  0x00007ffff65bb3b8 in QDoubleSpinBoxPrivate::textFromValue (this=0x1768890, f=...) at widgets/qspinbox.cpp:1279
#2  0x00007ffff64f9449 in QAbstractSpinBoxPrivate::updateEdit (this=0x1768890) at widgets/qabstractspinbox.cpp:1736
#3  0x00007ffff64f4e83 in QAbstractSpinBox::setLineEdit (this=0x1768860, lineEdit=0x1741840) at widgets/qabstractspinbox.cpp:686
#4  0x00007ffff64f87b9 in QAbstractSpinBoxPrivate::init (this=0x1768890) at widgets/qabstractspinbox.cpp:1558
#5  0x00007ffff64f401a in QAbstractSpinBox::QAbstractSpinBox (this=0x1768860, dd=..., parent=0x16bb7d0) at widgets/qabstractspinbox.cpp:152
#6  0x00007ffff65b8fae in QDoubleSpinBox::QDoubleSpinBox (this=0x1768860, parent=0x16bb7d0) at widgets/qspinbox.cpp:603
#7  0x00007ffff7283ab2 in qdesigner_internal::WidgetFactory::createWidget (this=0x8df9f0, widgetName=..., parentWidget=0x16bb7d0) at uilib/widgets.table:75
[...]
#41 0x00007ffff569706e in QEventLoop::exec (this=0x1489ac0, flags=...) at kernel/qeventloop.cpp:204
#42 0x00007ffff60d7438 in QDragManager::drag (this=0x1731a20, o=0x12b1780) at kernel/qdnd_x11.cpp:2028
#43 0x00007ffff6035bc1 in QDrag::exec (this=0x12b1780, supportedActions=..., defaultDropAction=Qt::CopyAction) at kernel/qdrag.cpp:284
[...]
#56 0x00007ffff66b53cd in QAbstractItemView::pressed (this=0x12b5f00, _t1=...) at .moc/debug-shared/moc_qabstractitemview.cpp:340
#57 0x00007ffff66a8b79 in QAbstractItemView::mousePressEvent (this=0x12b5f00, event=0x7fffffffcf90) at itemviews/qabstractitemview.cpp:1693
[...]
#68 0x00007ffff6024b9d in QCoreApplication::sendSpontaneousEvent (receiver=0x12b5f40, event=0x7fffffffcf90) at ../../include/QtCore/../../src/corelib/kernel/qcoreapplication.h:234
#69 0x00007ffff601eb61 in QApplicationPrivate::sendMouseEvent (receiver=0x12b5f40, event=0x7fffffffcf90, alienWidget=0x12b5f40, nativeWidget=0x95b2e0, buttonDown=0x7ffff6dbaa58,
    lastMouseReceiver=..., spontaneous=true) at kernel/qapplication.cpp:3171
[...]
#78 0x00007ffff5696ee4 in QEventLoop::processEvents (this=0x7fffffffddf0, flags=...) at kernel/qeventloop.cpp:149
#79 0x00007ffff569706e in QEventLoop::exec (this=0x7fffffffddf0, flags=...) at kernel/qeventloop.cpp:204
#80 0x00007ffff569a0b8 in QCoreApplication::exec () at kernel/qcoreapplication.cpp:1221
#81 0x00007ffff601f776 in QApplication::exec () at kernel/qapplication.cpp:3823
#82 0x0000000000432a07 in main (argc=1, argv=0x7fffffffdfa8) at main.cpp:57

Closes #349

Libs/Widgets/ctkCollapsibleButton.cpp

@@ -141,7 +141,13 @@ void ctkCollapsibleButtonPrivate::setChildVisibility(QWidget* childWidget)
     visible = false;
     }
 
-  childWidget->setVisible(visible);
+  // Setting Qt::WA_WState_Visible to true during child construction can have
+  // undesirable side effects.
+  if (childWidget->testAttribute(Qt::WA_WState_Created) ||
+      !visible)
+    {
+    childWidget->setVisible(visible);
+    }
 
   // setVisible() has set the ExplicitShowHide flag, restore it as we don't want
   // to make it like it was an explicit visible set because we want

Libs/Widgets/ctkCollapsibleGroupBox.cpp

@@ -93,7 +93,7 @@ public:
   /// who is changing children's visibility.
   bool     ForcingVisibility;
   /// Sometimes the creation of the widget is not done inside setVisible,
-  /// as we need to do special processing the first time the button is
+  /// as we need to do special processing the first time the groupBox is
   /// setVisible, we track its created state with the variable
   bool     IsStateCreated;
 
@@ -163,11 +163,17 @@ void ctkCollapsibleGroupBoxPrivate::setChildVisibility(QWidget* childWidget)
     visible = false;
     }
 
-  childWidget->setVisible(visible);
+  // Setting Qt::WA_WState_Visible to true during child construction can have
+  // undesirable side effects.
+  if (childWidget->testAttribute(Qt::WA_WState_Created) ||
+      !visible)
+    {
+    childWidget->setVisible(visible);
+    }
 
   // setVisible() has set the ExplicitShowHide flag, restore it as we don't want
   // to make it like it was an explicit visible set because we want
-  // to allow the children to be explicitly hidden by the user.
+  // to allow any children to be explicitly hidden by the user.
   if ((!childWidget->property("visibilityToParent").isValid() ||
       childWidget->property("visibilityToParent").toBool()))
     {