avcodec/nuv: zero buffer padding

Fixes use of uninitialized memory
Fixes msan_uninit-mem_7f4a141261de_7405_nirvana.nuv
Found-by: Mateusz "j00ru" Jurczyk and Gynvael Coldwind
Signed-off-by: Michael Niedermayer <michaelni@gmx.at>

libavcodec/nuv.c

@@ -218,6 +218,7 @@ retry:
         }
         buf      = c->decomp_buf;
         buf_size = c->decomp_size - FFMAX(FF_INPUT_BUFFER_PADDING_SIZE, AV_LZO_OUTPUT_PADDING) - outlen;
+        memset(c->decomp_buf + buf_size, 0, FF_INPUT_BUFFER_PADDING_SIZE);
     }
     if (c->codec_frameheader) {
         int w, h, q;