Delete empty cache files

When a cache filler function returns without success, we need to delete
the empty file we create so that it doesn't trigger a false positive the
next time we access it.

libsaria/cache.py

@@ -7,6 +7,7 @@ mkdir  = path.mkdir
 exists = path.exists
 join   = path.join
 ls     = path.ls
+rm     = path.rm
 
 CACHE_DIR = expand("~/.saria/cache")
 mkdir(CACHE_DIR)
@@ -26,6 +27,9 @@ class CacheObject:
 				pass
 			if success:
 				return path
+			else:
+				rm(path)
+
 		else:
 			return path