citra-qt: disable directory watcher during CIA installation (#4284)

* disable directory watcher during CIA installation

fixes several errors while installing multiple CIAs

* use braces in if statement

src/citra_qt/game_list.h

@@ -49,6 +49,7 @@ public:
     void clearFilter();
     void setFilterFocus();
     void setFilterVisible(bool visibility);
+    void setDirectoryWatcherEnabled(bool enabled);
     bool isEmpty();
 
     void LoadCompatibilityList();