Fix bug with the color source check in SweylaColorParser.
Fix bug with the color source check in SweylaColorParser.

SweylaColorParser's check was accepting any color source with number(s).
It would parse wallhaven.cc/wallpaper/427015 instead of
WallhavenColorParser, if it was declared before WallhavenColorParser in
the config file.

Also made the check in WallhavenColorParser stricter for consistency
with the other color parsers.

S0lll0s/themer,S0lll0s/themer