avcodec/simple_idct_template: Fix several integer overflows

Benchmarks with START_TIMER indicate that the code is faster with unsigned, (that is
with the patch), there was quite some fluctuation in the numbers so this may be just
random

Fixes: 811/clusterfuzz-testcase-6465493076541440

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

libavcodec/simple_idct_template.c

@@ -112,7 +112,7 @@ static inline void FUNC(idctRowCondDC_extrashift)(int16_t *row, int extra_shift)
 static inline void FUNC(idctRowCondDC)(int16_t *row, int extra_shift)
 #endif
 {
-    int a0, a1, a2, a3, b0, b1, b2, b3;
+    SUINT a0, a1, a2, a3, b0, b1, b2, b3;
 
 #if HAVE_FAST_64BIT
 #define ROW0_MASK (0xffffLL << 48 * HAVE_BIGENDIAN)
@@ -187,14 +187,14 @@ static inline void FUNC(idctRowCondDC)(int16_t *row, int extra_shift)
         MAC(b3, -W1, row[7]);
     }
 
-    row[0] = (a0 + b0) >> (ROW_SHIFT + extra_shift);
-    row[7] = (a0 - b0) >> (ROW_SHIFT + extra_shift);
-    row[1] = (a1 + b1) >> (ROW_SHIFT + extra_shift);
-    row[6] = (a1 - b1) >> (ROW_SHIFT + extra_shift);
-    row[2] = (a2 + b2) >> (ROW_SHIFT + extra_shift);
-    row[5] = (a2 - b2) >> (ROW_SHIFT + extra_shift);
-    row[3] = (a3 + b3) >> (ROW_SHIFT + extra_shift);
-    row[4] = (a3 - b3) >> (ROW_SHIFT + extra_shift);
+    row[0] = (int)(a0 + b0) >> (ROW_SHIFT + extra_shift);
+    row[7] = (int)(a0 - b0) >> (ROW_SHIFT + extra_shift);
+    row[1] = (int)(a1 + b1) >> (ROW_SHIFT + extra_shift);
+    row[6] = (int)(a1 - b1) >> (ROW_SHIFT + extra_shift);
+    row[2] = (int)(a2 + b2) >> (ROW_SHIFT + extra_shift);
+    row[5] = (int)(a2 - b2) >> (ROW_SHIFT + extra_shift);
+    row[3] = (int)(a3 + b3) >> (ROW_SHIFT + extra_shift);
+    row[4] = (int)(a3 - b3) >> (ROW_SHIFT + extra_shift);
 }
 
 #define IDCT_COLS do {                                  \
@@ -253,25 +253,25 @@ static inline void FUNC(idctSparseCol_extrashift)(int16_t *col)
 static inline void FUNC(idctSparseColPut)(pixel *dest, int line_size,
                                           int16_t *col)
 {
-    int a0, a1, a2, a3, b0, b1, b2, b3;
+    SUINT a0, a1, a2, a3, b0, b1, b2, b3;
 
     IDCT_COLS;
 
-    dest[0] = av_clip_pixel((a0 + b0) >> COL_SHIFT);
+    dest[0] = av_clip_pixel((int)(a0 + b0) >> COL_SHIFT);
     dest += line_size;
-    dest[0] = av_clip_pixel((a1 + b1) >> COL_SHIFT);
+    dest[0] = av_clip_pixel((int)(a1 + b1) >> COL_SHIFT);
     dest += line_size;
-    dest[0] = av_clip_pixel((a2 + b2) >> COL_SHIFT);
+    dest[0] = av_clip_pixel((int)(a2 + b2) >> COL_SHIFT);
     dest += line_size;
-    dest[0] = av_clip_pixel((a3 + b3) >> COL_SHIFT);
+    dest[0] = av_clip_pixel((int)(a3 + b3) >> COL_SHIFT);
     dest += line_size;
-    dest[0] = av_clip_pixel((a3 - b3) >> COL_SHIFT);
+    dest[0] = av_clip_pixel((int)(a3 - b3) >> COL_SHIFT);
     dest += line_size;
-    dest[0] = av_clip_pixel((a2 - b2) >> COL_SHIFT);
+    dest[0] = av_clip_pixel((int)(a2 - b2) >> COL_SHIFT);
     dest += line_size;
-    dest[0] = av_clip_pixel((a1 - b1) >> COL_SHIFT);
+    dest[0] = av_clip_pixel((int)(a1 - b1) >> COL_SHIFT);
     dest += line_size;
-    dest[0] = av_clip_pixel((a0 - b0) >> COL_SHIFT);
+    dest[0] = av_clip_pixel((int)(a0 - b0) >> COL_SHIFT);
 }
 
 static inline void FUNC(idctSparseColAdd)(pixel *dest, int line_size,