MINOR: mux-quic: do not set buffer for empty STREAM frame

Previous patch fixes an issue occurring with empty STREAM frames without
payload. The crash was hidden in part because buf/data fields of
qf_stream were set even if no payload is referenced. This was not the
true cause of the crash but to ease future debugging, a STREAM frame
built with no payload now has its buf and data fields set to NULL.

This should be backported up to 2.6.
1 file changed