encodebin: Also lock input caps when dynamic output is disabled

With the way caps negotiation work in encoders, the only way to ensure
that no downstream renegotiation is done in the encoder is to also lock
upstream caps. Anyway with the current behavior upstream of encoders
*require* to handle any file format so locking upstream format should
be safe.

https://bugzilla.gnome.org/show_bug.cgi?id=795464
1 file changed