image_writer: move tag_csp check into image_writer_flexible_csp()

This ensures the sRGB fallback to happen in all situations involving
the image writer code, notably --screenshot-sw.

fixes: cbbe2e5221

DOCS/man/options.rst

@@ -4334,11 +4334,11 @@ Screenshot
     :avif:      AVIF
 
 ``--screenshot-tag-colorspace=<yes|no>``
-    Tag screenshots with the appropriate colorspace.
+    Tag screenshots with the appropriate colorspace (default: yes).
 
-    Note that not all formats are supported.
-
-    Default: ``yes``.
+    Note that not all formats support this. When it is unsupported, or when
+    this option is disabled, screenshots will be converted to sRGB before
+    being written.
 
 ``--screenshot-high-bit-depth=<yes|no>``
     If possible, write screenshots with a bit depth similar to the source

player/screenshot.c

@@ -350,7 +350,7 @@ static struct mp_image *screenshot_get(struct MPContext *mpctx, int mode,
         .subs = mode != 0,
         .osd = mode == MODE_FULL_WINDOW,
         .high_bit_depth = high_depth && imgopts->high_bit_depth,
-        .native_csp = imgopts->tag_csp && image_writer_flexible_csp(imgopts),
+        .native_csp = image_writer_flexible_csp(imgopts),
     };
     if (!mpctx->opts->screenshot_sw)
         vo_control(mpctx->video_out, VOCTRL_SCREENSHOT, &ctrl);

video/image_writer.c

@@ -587,6 +587,8 @@ bool image_writer_high_depth(const struct image_writer_opts *opts)
 
 bool image_writer_flexible_csp(const struct image_writer_opts *opts)
 {
+    if (!opts->tag_csp)
+        return false;
     return false
 #if HAVE_JPEGXL
         || opts->format == AV_CODEC_ID_JPEGXL