indeo4: Decode all or nothing of a band header.

This avoids inconsistent value combinations.
Alternatively it would be possible to add more checks and careful use of
temporary variables, but my try of this quickly seemed to become
a rather large change.
The disadvantage of this, is that the struct is copied back and forth.

Fixes: index 6 out of bounds for type 'const uint16_t [5][16]'
Fixes: 6557/clusterfuzz-testcase-minimized-ffmpeg_AV_CODEC_ID_INDEO4_fuzzer-4787296550256640

Found-by: continuous fuzzing process https://github.com/google/oss-fuzz/tree/master/projects/ffmpeg
Signed-off-by: Michael Niedermayer <michael@niedermayer.cc>

libavcodec/indeo4.c

@@ -260,12 +260,14 @@ static int decode_pic_hdr(IVI45DecContext *ctx, AVCodecContext *avctx)
  *  @param[in]     avctx     pointer to the AVCodecContext
  *  @return        result code: 0 = OK, negative number = error
  */
-static int decode_band_hdr(IVI45DecContext *ctx, IVIBandDesc *band,
+static int decode_band_hdr(IVI45DecContext *ctx, IVIBandDesc *arg_band,
                            AVCodecContext *avctx)
 {
     int plane, band_num, indx, transform_id, scan_indx;
     int i;
     int quant_mat;
+    IVIBandDesc temp_band, *band = &temp_band;
+    memcpy(&temp_band, arg_band, sizeof(temp_band));
 
     plane    = get_bits(&ctx->gb, 2);
     band_num = get_bits(&ctx->gb, 4);
@@ -395,10 +397,10 @@ static int decode_band_hdr(IVI45DecContext *ctx, IVIBandDesc *band,
 
         /* decode block huffman codebook */
         if (!get_bits1(&ctx->gb))
-            band->blk_vlc.tab = ctx->blk_vlc.tab;
+            arg_band->blk_vlc.tab = ctx->blk_vlc.tab;
         else
             if (ff_ivi_dec_huff_desc(&ctx->gb, 1, IVI_BLK_HUFF,
-                                     &band->blk_vlc, avctx))
+                                     &arg_band->blk_vlc, avctx))
                 return AVERROR_INVALIDDATA;
 
         /* select appropriate rvmap table for this band */
@@ -439,6 +441,9 @@ static int decode_band_hdr(IVI45DecContext *ctx, IVIBandDesc *band,
         return AVERROR_INVALIDDATA;
     }
 
+    band->blk_vlc = arg_band->blk_vlc;
+    memcpy(arg_band, band, sizeof(*arg_band));
+
     return 0;
 }