Fix UB: Destoyed task is modified.

After destruction, task is no longer used, so updating its values is worthless.

src/battle_transition.c

@@ -4328,7 +4328,10 @@ static bool8 Phase2_FrontierSquaresScroll_Func5(struct Task *task)
     BlendPalettes(PALETTES_ALL, 0x10, 0);
 
     DestroyTask(FindTaskIdByFunc(task->func));
+
+#ifndef UBFIX
     task->tState++; // UB: changing value of a destroyed task
+#endif
     return FALSE;
 }