h264parse: Does not provide complete caps for alignment=nal in the beginning

Submitted by Sebastian Dröge @slomo

Link to original bug (#767778)

Description

When h264parse e.g. reads a raw bytestream h264 file, and as output alignment=nal is requested, it will first provide caps like video/x-h264,stream-format=... but without width/height/profile/etc.

It seems like it does not wait until it received the PPS/SPS in this mode before providing caps and outputting data, which it probably should.

In practice this is causing negotiation errors if there is an element that wants nal alignment but also requires width/height to be known in caps.