Fix a hack implemented in wxEnumProperty::ValueFromString_ and wxEnumProperty::ValueFromInt_ functions.

wxEnumProperty code is refactored in order to fix a hack which purpose was (apparently) to bypass constness of these functions by caching determined indices in wxEnumProperty::ms_nextIndex static member variable for further processing. (Unclear concept of using this static member was referred in http://trac.wxwidgets.org/ticket/12779#comment:9)
Now, determined index is returned to the caller and processed there if necessary and hence caching of this index is not necessary.

git-svn-id: https://svn.wxwidgets.org/svn/wx/wxWidgets/trunk@78390 c3d73ce0-8a6f-49c7-b76d-6d57e0e08775

src/propgrid/advprops.cpp

@@ -1454,13 +1454,11 @@ bool wxSystemColourProperty::StringToValue( wxVariant& value, const wxString& te
         {
             // This really should not occur...
             // wxASSERT(false);
-            ResetNextIndex();
             return false;
         }
 
         if ( !QueryColourFromUser(value) )
         {
-            ResetNextIndex();
             if ( !(argFlags & wxPG_PROPERTY_SPECIFIC) )
                 return false;
             // If query for value comes from the event handler
@@ -1477,12 +1475,11 @@ bool wxSystemColourProperty::StringToValue( wxVariant& value, const wxString& te
         if ( !conversionSuccess )
         {
             // Try predefined colour first
-            bool res = wxEnumProperty::StringToValue(value,
-                                                     colStr,
-                                                     argFlags);
-            if ( res && GetIndex() >= 0 )
+            int index;
+            bool res = ValueFromString_(value, &index, colStr, argFlags);
+            if ( res && index >= 0 )
             {
-                val.m_type = GetIndex();
+                val.m_type = index;
                 if ( val.m_type < m_choices.GetCount() )
                     val.m_type = m_choices[val.m_type].GetValue();
 
@@ -1501,7 +1498,6 @@ bool wxSystemColourProperty::StringToValue( wxVariant& value, const wxString& te
 
         if ( !done )
         {
-            ResetNextIndex();
             return false;
         }