avcodec/diracdec: Fix integer overflow in divide3()

Fixes: runtime error: signed integer overflow: -1073746548 * 21845 cannot be represented in type 'int'
Fixes: 2729/clusterfuzz-testcase-minimized-5902915464069120

Found-by: continuous fuzzing process https://github.com/google/oss-fuzz/tree/master/projects/ffmpegSigned-off-by: Michael Niedermayer <michael@niedermayer.cc>

libavcodec/diracdec.c

@@ -249,7 +249,7 @@ enum dirac_subband {
 /* magic number division by 3 from schroedinger */
 static inline int divide3(int x)
 {
-    return ((x+1)*21845 + 10922) >> 16;
+    return (int)((x+1U)*21845 + 10922) >> 16;
 }
 
 static DiracFrame *remove_frame(DiracFrame *framelist[], int picnum)