linecache.updatecache(): don't the lines into the cache on IOError

Use the same behaviour than Python 2.7.
diff --git a/Lib/linecache.py b/Lib/linecache.py
index f0bb83d..974b1d9 100644
--- a/Lib/linecache.py
+++ b/Lib/linecache.py
@@ -128,7 +128,7 @@
         with open(fullname, 'r', encoding=coding) as fp:
             lines = fp.readlines()
     except IOError:
-        lines = []
+        return []
     if lines and not lines[-1].endswith('\n'):
         lines[-1] += '\n'
     size, mtime = stat.st_size, stat.st_mtime