audio: Avoid bad pipelines from gst_parse_launch
audio: Avoid bad pipelines from gst_parse_launch

gst_parse_launch may return not NULL even when error is set.
This can lead to data loss when playing or recording audio.

freedesktop-unofficial-mirror/spice__spice-gtk,flexVDI/spice-gtk,freedesktop-unofficial-mirror/spice__spice-gtk,guodong/spice-gtk,freedesktop-unofficial-mirror/spice__spice-gtk,SPICE/spice-gtk,fgouget/spice-gtk,guodong/spice-gtk,Fantu/spice-gtk,SPICE/spice-gtk,fgouget/spice-gtk,elmarco/spice-gtk,SPICE/spice-gtk,Fantu/spice-gtk,Fantu/spice-gtk,SPICE/spice-gtk,fgouget/spice-gtk,guodong/spice-gtk,guodong/spice-gtk,elmarco/spice-gtk,Fantu/spice-gtk,flexVDI/spice-gtk,freedesktop-unofficial-mirror/spice__spice-gtk,elmarco/spice-gtk,elmarco/spice-gtk