Fix bug in combination of preferred and required content settings. When one was set to the empty string and the other set to some expression, this bug caused all files to be wanted, instead of only files matching the expression.

Avoid: MAny `MOr` otherexpression
Which matches anything.

Utility/Matcher.hs

@@ -27,6 +27,7 @@ module Utility.Matcher (
 	matchM,
 	matchMrun,
 	isEmpty,
+	combineMatchers,
 
 	prop_matcher_sane
 ) where
@@ -142,6 +143,14 @@ isEmpty :: Matcher a -> Bool
 isEmpty MAny = True
 isEmpty _ = False
 
+{- Combines two matchers, yielding a matcher that will match anything
+ - both do. -}
+combineMatchers :: Matcher a -> Matcher a -> Matcher a
+combineMatchers a b 
+	| isEmpty a = b
+	| isEmpty b = a
+	| otherwise = a `MOr` b
+
 prop_matcher_sane :: Bool
 prop_matcher_sane = all (\m -> match dummy m ()) $ map generate
 	[ [Operation True]