string_util: add function strchug_fast()

Replace g_strchug() calls with a cheaper implementation.

src/playlist/extm3u_playlist_plugin.c

@@ -24,6 +24,7 @@
 #include "uri.h"
 #include "song.h"
 #include "tag.h"
+#include "string_util.h"
 
 #include <glib.h>
 
@@ -89,7 +90,7 @@ extm3u_parse_tag(const char *line)
 		/* 0 means unknown duration */
 		duration = 0;
 
-	name = g_strchug(endptr + 1);
+	name = strchug_fast_c(endptr + 1);
 	if (*name == 0 && duration == 0)
 		/* no information available; don't allocate a tag
 		   object */