Fix #7098 by not accepting right clicks while dragging the range

(cherry picked from commit d40eb1565ed5a9cae29fa83561b42566119b2b7d)

scene/gui/tree.cpp

@@ -2388,6 +2388,9 @@ void Tree::_input_event(InputEvent p_event) {
 
 			}
 
+			if (range_drag_enabled)
+				break;
+
 			switch(b.button_index) {
 				case BUTTON_RIGHT:
 				case BUTTON_LEFT: {