Quant changes only once per MB so move the corresponding scale factor assignment

out of the block decoding loop. Indeo4 doesn't use any scale table but the quant
level itself as scale. Therefore access scale table only if its pointer != NULL.

Originally committed as revision 23569 to svn://svn.ffmpeg.org/ffmpeg/trunk

libavcodec/ivi_common.c

@@ -364,6 +364,8 @@ int ff_ivi_decode_blocks(GetBitContext *gb, IVIBandDesc *band, IVITile *tile)
 
         base_tab  = is_intra ? band->intra_base  : band->inter_base;
         scale_tab = is_intra ? band->intra_scale : band->inter_scale;
+        if (scale_tab)
+            quant = scale_tab[quant];
 
         if (!is_intra) {
             mv_x = mb->mv_x;
@@ -415,7 +417,7 @@ int ff_ivi_decode_blocks(GetBitContext *gb, IVIBandDesc *band, IVITile *tile)
                     if (IVI_DEBUG && !val)
                         av_log(NULL, AV_LOG_ERROR, "Val = 0 encountered!\n");
 
-                    q = (base_tab[pos] * scale_tab[quant]) >> 9;
+                    q = (base_tab[pos] * quant) >> 9;
                     if (q > 1)
                         val = val * q + FFSIGN(val) * (((q ^ 1) - 1) >> 1);
                     trvec[pos] = val;