Fix inspector window sometimes not hiding

When the f shortcut is quickly pressed, the inspector window will
sometimes open and remain open even though it should automatically
close. This commit ensures the window closes by capturing the f key
release event from the main window in addition to the inspector window.

rtgui/filecatalog.h

@@ -276,6 +276,7 @@ public:
     void openNextPreviousEditorImage (Glib::ustring fname, bool clearFilters, eRTNav nextPrevious);
 
     bool handleShortcutKey (GdkEventKey* event);
+    bool handleShortcutKeyRelease(GdkEventKey *event);
 
     bool CheckSidePanelsVisibility();
     void toggleSidePanels();