avcodec/shorten: Check k in get_uint()

Fixes: undefined shift
Fixes: 1371/clusterfuzz-testcase-minimized-5770822591447040

Found-by: continuous fuzzing process https://github.com/google/oss-fuzz/tree/master/targets/ffmpeg
Signed-off-by: Michael Niedermayer <michael@niedermayer.cc>
(cherry picked from commit 7b6a51f59c)
Signed-off-by: Michael Niedermayer <michael@niedermayer.cc>

libavcodec/shorten.c

@@ -155,8 +155,11 @@ static int allocate_buffers(ShortenContext *s)
 
 static inline unsigned int get_uint(ShortenContext *s, int k)
 {
-    if (s->version != 0)
+    if (s->version != 0) {
         k = get_ur_golomb_shorten(&s->gb, ULONGSIZE);
+        if (k > 31U)
+            return AVERROR_INVALIDDATA;
+    }
     return get_ur_golomb_shorten(&s->gb, k);
 }