gstplay: fix critical log when enable playbin3

gstplay: fix critical log when enable playbin3

when play rtsp stream with playbin3 enabled, there are some critical logs:

g_object_get_is_valid_property: object class 'GstPlayBin3' has no property named 'n-video'
g_object_get_is_valid_property: object class 'GstPlayBin3' has no property named 'n-audio'
g_object_get_is_valid_property: object class 'GstPlayBin3' has no property named 'n-text'

self->collection could be NULL when READY->PAUSED if the pipeline
is live, then it will fallback to query playbin2's property,
we can call gst_play_streams_info_create_from_collection
directly, it will check self->collection internal.

Part-of: <https://gitlab.freedesktop.org/gstreamer/gstreamer/-/merge_requests/4666>