BUG: commandlineparser - Handle the case when (ShortPrefix + UnPrefixedArg) matches LongPrefix

Also added associated regression test

Use case:
 setArgumentPrefix("--", "-");
 addArgument("ignore-rest", "-", QVariant::Bool, "This is an ignore flag");

The argument "--ignore-rest" was handled properly but "--" wasn't recognized
as shortprefix "-" associated with argument value "-".

Libs/Core/Testing/Cpp/ctkCommandLineParserTest1.cpp

@@ -339,6 +339,39 @@ int ctkCommandLineParserTest1(int, char*[])
     return EXIT_FAILURE;
     }
 
+  // Test7b - Same as Test7 using
+  ctkCommandLineParser parser7b;
+  parser7b.setArgumentPrefix("--", "-");
+  parser7b.addArgument("--bool", "-", QVariant::Bool, "This is a boolean",
+                      false /*defaultValue*/, true /* ignoreRest*/);
+  QStringList arguments7b;
+  arguments7b << "ctkCommandLineParserTest1";
+  arguments7b << "--";
+  arguments7b << expectedUnparsedArguments;
+
+  ok = false;
+  parsedArgs = parser7b.parseArguments(arguments7b, &ok);
+  if (!ok)
+    {
+    qCritical() << "Test7b - Failed to parse arguments";
+    return EXIT_FAILURE;
+    }
+  bool expectedTest7bBool = true;
+  bool test7bBool = parsedArgs["--bool"].toBool();
+  if (test7bBool != expectedTest7bBool)
+    {
+    qCritical() << "Test7b - Failed - test7bBool" << test7bBool
+        << ", expectedTest7bBool" << expectedTest7bBool;
+    return EXIT_FAILURE;
+    }
+
+  if (parser7b.unparsedArguments() != expectedUnparsedArguments)
+    {
+    qCritical() << "Test7b - Failed - expectedUnparsedArguments " << expectedUnparsedArguments
+                << ", parser7b.unparsedArguments" << parser7b.unparsedArguments();
+    return EXIT_FAILURE;
+    }
+
   // Test8 - Check if addStringArgument and ignore_rest=true works as expected
   ctkCommandLineParser parser8;
   parser8.addArgument("--string", "", QVariant::String, "This is a string",

Libs/Core/ctkCommandLineParser.cpp

@@ -239,7 +239,15 @@ CommandLineParserArgumentDescription*
   QString unprefixedArg = argument;
   if (!LongPrefix.isEmpty() && argument.startsWith(LongPrefix))
     {
-    unprefixedArg = argument.mid(LongPrefix.length());
+    // Case when (ShortPrefix + UnPrefixedArgument) matches LongPrefix
+    if (argument == LongPrefix && !ShortPrefix.isEmpty() && argument.startsWith(ShortPrefix))
+      {
+      unprefixedArg = argument.mid(ShortPrefix.length());
+      }
+    else
+      {
+      unprefixedArg = argument.mid(LongPrefix.length());
+      }
     }
   else if (!ShortPrefix.isEmpty() && argument.startsWith(ShortPrefix))
     {