demux/playlist: ProcessMRL: fallback to original if valid scheme
The changes introduced in
36bee77 had the unfortunate side-effect that
location-data that could not be parsed as a URL would be discarded,
for example an xspf playlist containing the line below would simply
ignore it (due to ProcessMRL rejecting it):
> dvb-t://frequency=
674000000:inversion=-1:bandwidth=8:code-rate-hp=2/3:code-rate-lp=1/2:modulation=64QAM:transmission=8:guard=1/32:
In order to fix the issue while still allowing uri-resolving for
URI-valid entities, the following changes make sure that we retain the
original string if it contains "://" and all prior characters are
valid in a scheme.
fixes: #18155
Signed-off-by: Jean-Baptiste Kempf <jb@videolan.org>