Only destroy damage_handle if a damage_handle got created

Summary:
Instead of binding to the OperationMode whether the damage_handle
should be destroyed, we bind it to whether damage_handle got created.

Reviewers: #plasma

Subscribers: plasma-devel

Projects: #plasma

Differential Revision: https://phabricator.kde.org/D1483

composite.cpp

@@ -998,7 +998,7 @@ void Toplevel::finishCompositing(ReleaseReason releaseReason)
         delete effect_window;
     }
 
-    if (kwinApp()->operationMode() == Application::OperationModeX11 &&
+    if (damage_handle != XCB_NONE &&
             releaseReason != ReleaseReason::Destroyed) {
         xcb_damage_destroy(connection(), damage_handle);
     }