ext/lame/gstlame.*: Fix the case where you initially have stereo input, and so lame...

ext/lame/gstlame.*: Fix the case where you initially have stereo input, and so lame's mode is not set to mono, and th...

Original commit message from CVS:
* ext/lame/gstlame.c:
* ext/lame/gstlame.h:
Fix the case where you initially have stereo input, and so lame's
mode is not set to mono, and then you get input with mono audio and
soon after you get stereo input again. What happened before this
commit is that it would keep the encoding mode as mono. It should
change it back to the one requested by the app (or the default one)
if not requested.