Avoid showing the colour selection dialog twice in wxPropertyGrid.

Selecting "Custom" in a colour property cell resulted in the colour selection
dialog being shown twice if it was cancelled the first time.

Fix this by using wxPG_PROPERTY_SPECIFIC to indicate that the value is just
being queried and the user shouldn't be asked to enter it, as it is already in
the other places.

Closes #15543.

git-svn-id: https://svn.wxwidgets.org/svn/wx/wxWidgets/trunk@76597 c3d73ce0-8a6f-49c7-b76d-6d57e0e08775

src/propgrid/editors.cpp

@@ -1277,7 +1277,7 @@ bool wxPGComboBoxEditor::GetValueFromControl( wxVariant& variant, wxPGProperty*
         return true;
     }
 
-    bool res = property->StringToValue(variant, textVal, wxPG_EDITABLE_VALUE);
+    bool res = property->StringToValue(variant, textVal, wxPG_EDITABLE_VALUE|wxPG_PROPERTY_SPECIFIC);
 
     // Changing unspecified always causes event (returning
     // true here should be enough to trigger it).