vo_corevideo: fix regression in colormatrix handling

Regression since 18b6c01d92. That commit changed the colorspace handling to
always reinit the video output. Since the CVPixelBuffers are lazily created,
VOCTRL_SET_YUV_COLORSPACE was always called when the CVPixelBufferRef was NULL.

Since CoreVideo functions do not complain when called on NULL, no one noticed
that CVBufferSetAttachment, which stored the color matrix meta data was called
on NULL.
configure: fix help for macosx-bundle from autodetected to disabled

The help and configure result wrongly showed this feature was autodetected,
while it is infact disabled by default.