video: skip 'text' gfxpayload if not supported, to fallback to default

On UEFI, 'text' gfxpayload is not supported, but we still reach parse_modespec()
with it, which will obviously fail. Fortunately, whatever gfxpayload is set,
we still still have the 'auto' default to fall back to. Allow getting to this
fallback by not trying to parse 'text' as a modespec.

This is because 'text' correctly doesn't parse as a modespec, and ought to have
been ignored before we got to that point, just like it is immediately picked if
we're running on a system where 'text' is a supported video mode.

Bug: https://savannah.gnu.org/bugs/index.php?56217

Signed-off-by: Mathieu Trudel-Lapierre <mathieu.trudel-lapierre@canonical.com>
Reviewed-by: Daniel Kiper <daniel.kiper@oracle.com>

grub-core/video/video.c

@@ -663,6 +663,8 @@ grub_video_set_mode (const char *modestring,
 
 	      return GRUB_ERR_NONE;
 	    }
+	  else
+	    continue;
 	}
 
       err = parse_modespec (current_mode, &width, &height, &depth);