Fix T87637: Dragging button value cancel not working

Dragging a number button, then holding the value and pressing escape
would not reset the value correctly.
This was because eb06ccc324 assumed that `data->value` and
`data->startvalue` were set during dragging which they are not.

The fix moves the if statement into the section where we check if a
number was entered (number edit) making sure that we only cancel
if the button was in "string enter" mode and that the value entered
was the same as before.

Reviewed By: HooglyBoogly, Severin

Maniphest Tasks: T87637

Differential Revision: https://developer.blender.org/D11021

source/blender/editors/interface/interface_handlers.c

@@ -1121,17 +1121,17 @@ static void ui_apply_but_NUM(bContext *C, uiBut *but, uiHandleButtonData *data)
       data->cancel = true;
       return;
     }
+
+    /* If the value entered is the exact same, do not trigger an update. */
+    if (data->value == data->startvalue) {
+      data->cancel = true;
+      return;
+    }
   }
   else {
     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);