swscale/yuv2rgb: Increase YUV2RGB table headroom

This makes SWS more robust
Fixes: 07650a772d98aa63b0fed6370dc89037/asan_heap-oob_27ddeaf_2657_2c81ff264dee5d9712cb3251fb9c3bbb.264
Fixes: out of array read

Found-by: Mateusz "j00ru" Jurczyk and Gynvael Coldwind
Signed-off-by: Michael Niedermayer <michael@niedermayer.cc>

libswscale/swscale_internal.h

@@ -39,8 +39,8 @@
 
 #define STR(s) AV_TOSTRING(s) // AV_STRINGIFY is too long
 
-#define YUVRGB_TABLE_HEADROOM 256
-#define YUVRGB_TABLE_LUMA_HEADROOM 0
+#define YUVRGB_TABLE_HEADROOM 512
+#define YUVRGB_TABLE_LUMA_HEADROOM 512
 
 #define MAX_FILTER_SIZE SWS_MAX_FILTER_SIZE