avcodec/diracdec: Check perspective_exp and zrs_exp.

Fixes: undefined shift
Fixes: runtime error: shift exponent 264 is too large for 32-bit type 'int'
Fixes: 2860/clusterfuzz-testcase-minimized-4672811689836544

Found-by: continuous fuzzing process https://github.com/google/oss-fuzz/tree/master/projects/ffmpeg
Signed-off-by: Michael Niedermayer <michael@niedermayer.cc>
(cherry picked from commit 1e6cab8745)
Signed-off-by: Michael Niedermayer <michael@niedermayer.cc>

libavcodec/diracdec.c

@@ -960,6 +960,10 @@ static int dirac_unpack_prediction_parameters(DiracContext *s)
                 s->globalmc[ref].perspective[0]  = dirac_get_se_golomb(gb);
                 s->globalmc[ref].perspective[1]  = dirac_get_se_golomb(gb);
             }
+            if (s->globalmc[ref].perspective_exp + (uint64_t)s->globalmc[ref].zrs_exp > 30) {
+                return AVERROR_INVALIDDATA;
+            }
+
         }
     }