macosx: only scan optical devices paths once and cache the result

modules/gui/macosx/open.h

@@ -235,6 +235,7 @@
     BOOL b_nodvdmenus;
     id o_currentOpticalMediaView;
     id o_currentOpticalMediaIconView;
+    NSMutableArray *o_allMediaDevices;
     NSMutableArray *o_opticalDevices;
     NSMutableArray *o_specialMediaFolders;
     NSString *o_file_path;