vaapisink: ignore frame if its upload failed

vaapisink: ignore frame if its upload failed

When gst_vaapi_plugin_base_get_input_buffer() fail to copy the input buffer
into a VAAPI buffer, the return value is GST_FLOW_NOT_SUPPORTED, and it was
ignored by the vaapisink, leading to a segmentation fault.

This patch ignores the frame that generated the GST_FLOW_NOT_SUPPORTED
returned by gst_vaapi_plugin_base_get_input_buffer(), avoiding the
segmentation fault, but doing and effort to continue rendering. This is
the same behavior of ximagesink.

Signed-off-by: Víctor Manuel Jáquez Leal <victorx.jaquez@intel.com>
https://bugzilla.gnome.org/show_bug.cgi?id=759332