RA144: work around gcc bug/oddity on ARM

This should not make any difference, yet some gcc versions on ARM
produce incorrect output without this fix.

Approved by Vitor.

Originally committed as revision 17698 to svn://svn.ffmpeg.org/ffmpeg/trunk

libavcodec/ra144.c

@@ -200,7 +200,7 @@ static void do_output_subblock(RA144Context *ractx, const uint16_t  *lpc_coefs,
 
     block = ractx->adapt_cb + BUFFERSIZE - BLOCKSIZE;
 
-    add_wav(block, gain, cba_idx, m, buffer_a,
+    add_wav(block, gain, cba_idx, m, cba_idx? buffer_a: NULL,
             cb1_vects[cb1_idx], cb2_vects[cb2_idx]);
 
     memcpy(ractx->curr_sblock, ractx->curr_sblock + 40,