narrowspec: use vfs.tryread() instead of reimplementing

Note that parseconfig() works well with empty strings.

Differential Revision: https://phab.mercurial-scm.org/D6465

mercurial/narrowspec.py

@@ -7,8 +7,6 b''
 
 from __future__ import absolute_import
 
-import errno
-
 from .i18n import _
 from . import (
     error,
@@ -145,15 +143,9 b' def parseconfig(ui, spec):'
     return includepats, excludepats
 
 def load(repo):
-    try:
-        spec = repo.svfs.read(FILENAME)
-    except IOError as e:
         # Treat "narrowspec does not exist" the same as "narrowspec file exists
         # and is empty".
-        if e.errno == errno.ENOENT:
-            return set(), set()
-        raise
-
+    spec = repo.svfs.tryread(FILENAME)
     return parseconfig(repo.ui, spec)
 
 def save(repo, includepats, excludepats):