Debugger: Slight tweak to changed value highlighting.

VariablesView::ModelNode:
- Only check if a variable's value has changed if we actually have a
  valid previous value to compare against. Otherwise, e.g. variables
  that just came into scope but haven't yet been initialized would
  show up as changed, while their value is, at that point completely
  uninteresting.

src/apps/debugger/user_interface/gui/team_window/VariablesView.cpp

@@ -354,9 +354,8 @@ private:
 private:
 	void _CompareValues()
 	{
-		if (fValue == NULL)
-			fValueChanged = false;
-		else {
+		fValueChanged = false;
+		if (fValue != NULL && fPreviousValue.Type() != 0) {
 			BVariant newValue;
 			fValue->ToVariant(newValue);
 			fValueChanged = (fPreviousValue != newValue);