Don't set maximum text length for non-text wxPG properties

Setting the limit for the length of the text the user can enter in the text editor makes sense only for properties having text editors so in wxPGProperty::SetMaxLength() should be done a check whether to actually set a limit or not depending on the kind of editor used.
wxPropertyGridInterface::SetPropertyMaxLength() should be implemented on top of wxPGProperty::SetMaxLength() to proceed only if maximum length was actually set.

interface/wx/propgrid/propgridiface.h

@@ -1053,7 +1053,19 @@ public:
     void SetPropertyImage( wxPGPropArg id, wxBitmap& bmp );
 
     /**
-        Sets max length of property's text.
+        Sets maximum length of text in property text editor.
+
+        @param id
+            Property name or pointer.
+        @param maxLen
+            Maximum number of characters of the text the user can enter in
+            the text editor. If it is 0, the length is not limited and the text
+            can be as long as it is supported by the the underlying native text
+            control widget.
+        @return
+            Returns @true if maximum length was set.
+        @see
+            wxPGProperty::SetMaxLength.
     */
     bool SetPropertyMaxLength( wxPGPropArg id, int maxLen );