avcodec/interplayacm: Fix integer overflows in juggle()

Fixes: signed integer overflow: -760459023 + -1520918047 cannot be represented in type 'int'
Fixes: 17994/clusterfuzz-testcase-minimized-ffmpeg_AV_CODEC_ID_INTERPLAY_ACM_fuzzer-5647123042795520

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

libavcodec/interplayacm.c

@@ -435,7 +435,8 @@ static int fill_block(InterplayACMContext *s)
 static void juggle(int *wrap_p, int *block_p, unsigned sub_len, unsigned sub_count)
 {
     unsigned i, j;
-    int *p, r0, r1, r2, r3;
+    int *p;
+    unsigned int r0, r1, r2, r3;
 
     for (i = 0; i < sub_len; i++) {
         p = block_p;