Fix T87448: Avoid uiBut update if value was same

Previously, clicking into a number field, changing nothing and then
clicking outside the field again would trigger an update (RNA prop
would be set to the same value again). This could potentially cause
an expensive operation (like a modifer) to run again, even if all the
parameters were identical.

The fix prevents this by treating unchanging values in the field as a
cancel operation.

Reviewed By: Severin

Maniphest Tasks: T87448

Differential Revision: https://developer.blender.org/D10976

source/blender/editors/interface/interface_handlers.c

@@ -1126,6 +1126,12 @@ static void ui_apply_but_NUM(bContext *C, uiBut *but, uiHandleButtonData *data)
     ui_but_value_set(but, data->value);
   }
 
+  /* If the value entered is the exact same, do not trigger an update. */
+  if (data->value == data->startvalue) {
+    data->cancel = true;
+    return;
+  }
+
   ui_but_update_edited(but);
   ui_apply_but_func(C, but);