swscale: avoid invalid pointer conversion

(cherry picked from commit ab00e6c59d)
Signed-off-by: Thomas Guillem <thomas@gllm.fr>

modules/video_chroma/swscale.c

@@ -588,8 +588,9 @@ static void Convert( filter_t *p_filter, struct SwsContext *ctx,
 {
     filter_sys_t *p_sys = p_filter->p_sys;
     uint8_t palette[AVPALETTE_SIZE];
-    uint8_t *src[4]; int src_stride[4];
-    uint8_t *dst[4]; int dst_stride[4];
+    uint8_t *src[4], *dst[4];
+    const uint8_t *csrc[4];
+    int src_stride[4], dst_stride[4];
 
     GetPixels( src, src_stride, p_sys->desc_in, &p_filter->fmt_in.video,
                p_src, i_plane_count, b_swap_uvi );
@@ -606,11 +607,14 @@ static void Convert( filter_t *p_filter, struct SwsContext *ctx,
     GetPixels( dst, dst_stride, p_sys->desc_out, &p_filter->fmt_out.video,
                p_dst, i_plane_count, b_swap_uvo );
 
+    for (size_t i = 0; i < ARRAY_SIZE(src); i++)
+        csrc[i] = src[i];
+
 #if LIBSWSCALE_VERSION_INT  >= ((0<<16)+(5<<8)+0)
-    sws_scale( ctx, src, src_stride, 0, i_height,
+    sws_scale( ctx, csrc, src_stride, 0, i_height,
                dst, dst_stride );
 #else
-    sws_scale_ordered( ctx, src, src_stride, 0, i_height,
+    sws_scale_ordered( ctx, csrc, src_stride, 0, i_height,
                        dst, dst_stride );
 #endif
 }