make ext_workspace_unstable impl more atomic (#2023)

src/managers/KeybindManager.cpp

@@ -960,6 +960,9 @@ void CKeybindManager::changeworkspace(std::string args) {
     if (ANOTHERMONITOR)
         g_pCompositor->warpCursorTo(PMONITOR->vecPosition + PMONITOR->vecSize / 2.f);
 
+    // Destroy old workspace if it is empty
+    g_pCompositor->sanityCheckWorkspaces();
+
     Debug::log(LOG, "Changed to workspace %i", workspaceToChangeTo);
 }