swscale/input: Use unsigned intermediates in rgb64ToUV_c_template

Large rgb2yuv tables and high pixel values cause the intermediate
int32_t of ru*r + gu*g + bu*b to exceed INT_MAX, which is undefined
behavior. This causes libswscale built with LLVM -fsanitize=undefined to
assert. Using unsigned integers instead has defined behavior and
produces identical results, and makes rgb64ToUV_c_template match
rgb64ToY_c_template.

Fixes: signed integer overflow
Signed-off-by: Michael Niedermayer <michael@niedermayer.cc>

libswscale/input.c

@@ -65,9 +65,9 @@ rgb64ToUV_c_template(uint16_t *dstU, uint16_t *dstV,
     int32_t rv = rgb2yuv[RV_IDX], gv = rgb2yuv[GV_IDX], bv = rgb2yuv[BV_IDX];
     av_assert1(src1==src2);
     for (i = 0; i < width; i++) {
-        int r_b = input_pixel(&src1[i*4+0]);
-        int   g = input_pixel(&src1[i*4+1]);
-        int b_r = input_pixel(&src1[i*4+2]);
+        unsigned int r_b = input_pixel(&src1[i*4+0]);
+        unsigned int   g = input_pixel(&src1[i*4+1]);
+        unsigned int b_r = input_pixel(&src1[i*4+2]);
 
         dstU[i] = (ru*r + gu*g + bu*b + (0x10001<<(RGB2YUV_SHIFT-1))) >> RGB2YUV_SHIFT;
         dstV[i] = (rv*r + gv*g + bv*b + (0x10001<<(RGB2YUV_SHIFT-1))) >> RGB2YUV_SHIFT;