song/StringFilter: move negated flag from containing class

src/song/StringFilter.cxx

@@ -23,8 +23,8 @@
 
 #include <assert.h>
 
-bool
-StringFilter::Match(const char *s) const noexcept
+inline bool
+StringFilter::MatchWithoutNegation(const char *s) const noexcept
 {
 #if !CLANG_CHECK_VERSION(3,6)
 	/* disabled on clang due to -Wtautological-pointer-compare */
@@ -41,3 +41,9 @@ StringFilter::Match(const char *s) const noexcept
 			: value == s;
 	}
 }
+
+bool
+StringFilter::Match(const char *s) const noexcept
+{
+	return MatchWithoutNegation(s) != negated;
+}