macosx: fix possible SPMediaKeyTap crash

Adding nil to an NSArray would make it raise an
NSInvalidArgumentException which in turn leads to an abort in
dispatch_once:
  https://github.com/apple-oss-distributions/libdispatch/blob/55c3a68e9ec47f1c1d5bb9909404ce5f0351edef/src/object.m#L557

Fix #27487