swscale/output: Fix integer overflow in yuv2rgb_write_full() with out of range input

Fixes: signed integer overflow: 1169365504 + 981452800 cannot be represented in type 'int'
Fixes: ticket8293

Found-by: Suhwan
Signed-off-by: Michael Niedermayer <michael@niedermayer.cc>

libswscale/output.c

@@ -1850,9 +1850,9 @@ static av_always_inline void yuv2rgb_write_full(SwsContext *c,
     Y -= c->yuv2rgb_y_offset;
     Y *= c->yuv2rgb_y_coeff;
     Y += 1 << 21;
-    R = Y + V*c->yuv2rgb_v2r_coeff;
-    G = Y + V*c->yuv2rgb_v2g_coeff + U*c->yuv2rgb_u2g_coeff;
-    B = Y +                          U*c->yuv2rgb_u2b_coeff;
+    R = (unsigned)Y + V*c->yuv2rgb_v2r_coeff;
+    G = (unsigned)Y + V*c->yuv2rgb_v2g_coeff + U*c->yuv2rgb_u2g_coeff;
+    B = (unsigned)Y +                          U*c->yuv2rgb_u2b_coeff;
     if ((R | G | B) & 0xC0000000) {
         R = av_clip_uintp2(R, 30);
         G = av_clip_uintp2(G, 30);