avcodec/lagarith: Check dst/src in zero run code

Fixes: out of array access
Fixes: 48799/clusterfuzz-testcase-minimized-ffmpeg_AV_CODEC_ID_LAGARITH_fuzzer-4764457825337344

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

libavcodec/lagarith.c

@@ -409,6 +409,9 @@ output_zeros:
         if (zero_run) {
             zero_run = 0;
             i += esc_count;
+            if (i >  end - dst ||
+                i >= src_end - src)
+                return AVERROR_INVALIDDATA;
             memcpy(dst, src, i);
             dst += i;
             l->zeros_rem = lag_calc_zero_run(src[i]);