avcodec/lagarith: disable lag_decode_zero_run_line() and ask for a sample

The code seems to have never been tested
fixing it should be quite easy but needs a sample/testcase

Fixes use of uninitialized memory
Fixes: msan_uninit-mem_7f9a862dfabf_413_2889_assassin_OL.avi
Found-by: Mateusz "j00ru" Jurczyk and Gynvael Coldwind
Signed-off-by: Michael Niedermayer <michaelni@gmx.at>

libavcodec/lagarith.c

@@ -369,6 +369,9 @@ static int lag_decode_zero_run_line(LagarithContext *l, uint8_t *dst,
     uint8_t mask2 = -(esc_count < 3);
     uint8_t *end = dst + (width - 2);
 
+    avpriv_request_sample(l->avctx, "zero_run_line");
+    return AVERROR_PATCHWELCOME;
+
 output_zeros:
     if (l->zeros_rem) {
         count = FFMIN(l->zeros_rem, width - i);