avutil/error: Fix overflow when negating

-INT_MIN is not representable in an int.
Fixes issue #22388.

Reviewed-by: Sean McGovern <gseanmcg@gmail.com>
Signed-off-by: Andreas Rheinhardt <andreas.rheinhardt@outlook.com>

libavutil/error.c

@@ -140,7 +140,7 @@ int av_strerror(int errnum, char *errbuf, size_t errbuf_size)
         }
     }
 #if HAVE_STRERROR_R
-    int ret = AVERROR(strerror_r(AVUNERROR(errnum), errbuf, errbuf_size));
+    int ret = AVERROR(strerror_r(AVUNERROR((unsigned)errnum), errbuf, errbuf_size));
 #else
     int ret = -1;
 #endif