avcodec/msmpeg4dec: Don't initialize unused RL VLCs

For the RLTables ff_rl_table[0..2] only the very first VLC is only ever
used, so it makes no sense to create 32 of them. This saves 285200B from
the .bss segment; this amount of memory is actually saved when this
decoder is used.

Signed-off-by: Andreas Rheinhardt <andreas.rheinhardt@gmail.com>
