fs-rtp-substream: Don't leak caps on error
fs-rtp-substream: Don't leak caps on error

Based on patch from Havard Graff

pexip/farstream,kakaroto/farstream,tieto/farstream,pexip/farstream,tieto/farstream,tieto/farstream,tieto/farstream,kakaroto/farstream,tieto/farstream,kakaroto/farstream,pexip/farstream,pexip/farstream,kakaroto/farstream