Cache should check for success of func()

We return after checking if the fetcher function succeeds.  To do this
properly, we should store the value we get so that the cached file can
be closed before returning.

libsaria/cache.py

@@ -19,12 +19,13 @@ class CacheObject:
 		path = join(self.path, key)
 		if not exists(path):
 			f = open(path, 'w')
-			if func(f, *args):
-				return path
+			success = func(f, *args)
 			try:
 				f.close()
 			except:
 				pass
+			if success:
+				return path
 		else:
 			return path