-af channels=nb breaks stop/restart

[cognet@…]

When the command line is treated in af_create(), it uses strsep() to split it.
But strsep() will replace the = by a \0, so the next time af_create() gets called,
typically when stopping then restarting the video, the command line will be
"channels" instead of "channels=2", and later af_channel.c will barf that the
channels number is 0, while it should at least be 1.
The attached patch just re-change the \0 to a '=' once we can do it.

[cognet@…]

The patch mentionned in the original text