avcodec/dirac_dwt: Fix overflows in COMPOSE_HAARiH0/COMPOSE_HAARiL0

Fixes: 4830/clusterfuzz-testcase-minimized-5255392054476800
Fixes: signed integer overflow: 2147483646 - -7 cannot be represented in type 'int'

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 0e62a23734)
Signed-off-by: Michael Niedermayer <michael@niedermayer.cc>

libavcodec/dirac_dwt.h

@@ -96,10 +96,10 @@ void ff_spatial_idwt_slice2(DWTContext *d, int y);
     (int)(((unsigned)(b2) - ((int)(-b0 + 9U*b1 + 9U*b3 - b4 + 16) >> 5)))
 
 #define COMPOSE_HAARiL0(b0, b1)\
-    (b0 - ((b1 + 1) >> 1))
+    ((int)(b0 - (unsigned)((int)(b1 + 1U) >> 1)))
 
 #define COMPOSE_HAARiH0(b0, b1)\
-    (b0 + b1)
+    ((int)(b0 + (unsigned)(b1)))
 
 #define COMPOSE_FIDELITYiL0(b0, b1, b2, b3, b4, b5, b6, b7, b8)\
     ((unsigned)b4 - ((int)(-8*(b0+(unsigned)b8) + 21*(b1+(unsigned)b7) - 46*(b2+(unsigned)b6) + 161*(b3+(unsigned)b5) + 128) >> 8))