mvcdec: Heap overflow in 'ih264d_read_coeff4x4_cabac'

In some erroneous fuzzer bistreams, the slice data requires more
parsing than what was implied by the distance between successive
start codes. The primary culprit is the NEXTBITS macro which requires
reading 4 additional bytes of the bitstream buffer. To alleviate
this, 16 bytes per 4x4 TU have been additionally allocated to the
bitstream buffer. Also, chroma bytes are added for 4:2:0/4:2:2.

This is in reference to commit-72315c1, where additional bytes were added to fix similar issue.

Bug = ossfuzz:42538616
Test: mvc_dec_fuzzer

decoder/mvc/imvcd_api.c

@@ -737,9 +737,10 @@ static IV_API_CALL_STATUS_T imvcd_view_decode(iv_obj_t *ps_dec_hdl, imvcd_video_
               parsing than what was implied by the distance between successive
               start codes.The primary culprit is the NEXTBITS macro which requires
               reading 4 additional bytes of the bitstream buffer.To alleviate
-              this, 4 bytes per 4x4 TU have been additionally allocated to the
-              bitstream buffer. */
-            UWORD32 u4_nalu_buf_size = ((UWORD32) i4_nalu_length) + 8 + 4 * 16;
+              this, 16 bytes per 4x4 TU have been additionally allocated to the
+              bitstream buffer. Also, chroma bytes are added for 4:2:0/4:2:2 */
+
+            UWORD32 u4_nalu_buf_size = ((UWORD32) i4_nalu_length) + 8 + EXTRA_BS_OFFSET;
 
             if(u4_nalu_buf_size > u4_bitstream_buf_size)
             {