swscale: treat XYZ formats as colorspace-less in color (de|en)coding

XYZ formats carry no YCbCr matrix, so decode and encode them like RGB
instead of falling into the unspecified colorspace path, which applied
a BT.470BG matrix and marked the graph as incomplete.

Note that the new code does not yet convert between XYZ and RGB.

libswscale/format.c

@@ -1522,8 +1522,10 @@ int ff_sws_decode_colors(SwsContext *ctx, SwsPixelType type,
         .lin  = fmt_decode_range(fmt, incomplete),
     }));
 
-    /* Final step, decode colorspace */
-    switch (fmt->csp) {
+    /* Final step, decode colorspace. XYZ formats carry no colorspace
+     * matrix; their transfer/primaries are handled by the color mapping
+     * layer, so treat them like RGB here. */
+    switch (fmt->desc->flags & AV_PIX_FMT_FLAG_XYZ ? AVCOL_SPC_RGB : fmt->csp) {
     case AVCOL_SPC_RGB:
         return 0;
     case AVCOL_SPC_UNSPECIFIED:
@@ -1595,7 +1597,8 @@ int ff_sws_encode_colors(SwsContext *ctx, SwsPixelType type,
     if (!pixel_type)
          return AVERROR(ENOTSUP);
 
-    switch (dst->csp) {
+    /* See ff_sws_decode_colors(): XYZ formats have no colorspace matrix */
+    switch (dst->desc->flags & AV_PIX_FMT_FLAG_XYZ ? AVCOL_SPC_RGB : dst->csp) {
     case AVCOL_SPC_RGB:
         break;
     case AVCOL_SPC_UNSPECIFIED:

tests/ref/fate/sws-ops-list

@@ -1 +1 @@
-b4ea23c724f642b3e43d329ed4981d38
+1f03295f230be02367e812f3670230cc