Fixed forum-17249: NullReferenceException in MergeFormChanges if the form contains a VB field without datatype.

git-svn-id: svn://svn.sharpdevelop.net/sharpdevelop/branches/2.1@2537 1ccf3a8d-04fe-1044-b7c0-cef0b8235c61

src/AddIns/DisplayBindings/FormsDesigner/Project/Src/DesignerGenerator/AbstractDesignerGenerator.cs

@@ -231,10 +231,12 @@ namespace ICSharpCode.FormsDesigner
 		bool FieldChanged(IField oldField, CodeMemberField newField)
 		{
 			// compare types
+			if (oldField.ReturnType != null) { // ignore type changes to untyped VB fields
 				if (oldField.ReturnType.FullyQualifiedName != newField.Type.BaseType) {
 					LoggingService.Debug("FieldChanged: "+oldField.Name+", "+oldField.ReturnType.FullyQualifiedName+" -> "+newField.Type.BaseType);
 					return true;
 				}
+			}
 			
 			// compare modifiers
 			ModifierEnum oldModifiers = oldField.Modifiers & ModifierEnum.VisibilityMask;