convert no-profile CMYK to RGB on save

Use the fallback cmyk profile to convert to RGB on save if the image has
no embedded profile.

Thanks augustocdias.

See https://github.com/libvips/libvips/issues/1767

ChangeLog

@@ -3,6 +3,7 @@
 - remove typedef redefinitions to please old gccs
 - fix regression in tiff pyramid thumbnailing [tand826]
 - stop 0-length buffer being passed to imagemagick [lovell]
+- convert no-profile CMYK to RGB on save [augustocdias]
 
 24/1/20 started 8.10.0
 - more conformat IIIF output from dzsave [regisrob]

libvips/foreign/foreign.c

@@ -1336,8 +1336,7 @@ vips__foreign_convert_saveable( VipsImage *in, VipsImage **ready,
 	}
 
 	/* If this image is CMYK and the saver is RGB-only, use lcms to try to
-	 * import to XYZ. This will only work if the image has an embedded
-	 * profile. 
+	 * import to XYZ. 
 	 */
 	if( in->Type == VIPS_INTERPRETATION_CMYK &&
 		in->Bands >= 4 &&
@@ -1348,6 +1347,8 @@ vips__foreign_convert_saveable( VipsImage *in, VipsImage **ready,
 
 		if( vips_icc_import( in, &out, 
 			"pcs", VIPS_PCS_XYZ,
+			"embedded", TRUE,
+			"input_profile", "cmyk",
 			NULL ) ) {
 			g_object_unref( in );
 			return( -1 );