avcodec/dirac_dwt: Fix integer overflow in COMPOSE_53iL0()

Fixes: runtime error: signed integer overflow: 2147483646 + 2 cannot be represented in type 'int'
Fixes: 3485/clusterfuzz-testcase-minimized-4940429332054016

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

libavcodec/dirac_dwt.h

@@ -93,10 +93,10 @@ void ff_spatial_idwt_slice2(DWTContext *d, int y);
 
 // shared stuff for simd optimizations
 #define COMPOSE_53iL0(b0, b1, b2)\
-    (b1 - ((b0 + b2 + 2) >> 2))
+    (b1 - ((int)(b0 + (unsigned)(b2) + 2) >> 2))
 
 #define COMPOSE_DIRAC53iH0(b0, b1, b2)\
-    (b1 + ((b0 + b2 + 1) >> 1))
+    (b1 + ((int)(b0 + (unsigned)(b2) + 1) >> 1))
 
 #define COMPOSE_DD97iH0(b0, b1, b2, b3, b4)\
     (b2 + ((int)(-b0 + 9U*b1 + 9U*b3 - b4 + 8) >> 4))