avcodec/aacdec_template: Fix undefined signed interger operations

Fixed: signed integer overflow: -2 * -1085502286 cannot be represented in type 'int'
Fixed: 57986/clusterfuzz-testcase-minimized-ffmpeg_AV_CODEC_ID_AAC_FIXED_fuzzer-5123651145170944

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 87f76d3bee)
Signed-off-by: Michael Niedermayer <michael@niedermayer.cc>

libavcodec/aacdec_template.c

@@ -2856,8 +2856,8 @@ static void imdct_and_windowing_eld(AACContext *ac, SingleChannelElement *sce)
         ac->mdct512_fn(ac->mdct512, buf, in, sizeof(INTFLOAT));
 
     for (i = 0; i < n; i+=2) {
-        buf[i + 0] = -(USE_FIXED + 1)*buf[i + 0];
-        buf[i + 1] =  (USE_FIXED + 1)*buf[i + 1];
+        buf[i + 0] = -(int)(USE_FIXED + 1U)*buf[i + 0];
+        buf[i + 1] =  (int)(USE_FIXED + 1U)*buf[i + 1];
     }
     // Like with the regular IMDCT at this point we still have the middle half
     // of a transform but with even symmetry on the left and odd symmetry on