shelve: trust caller of shelvedfile.opener() to check that the file exists

The only place we call `shelvedfile.opener()` is when we're about to
apply a bundle. The file should always exist. If it doesn't, the
`.hg/` directory is corrupt and we don't provide any guarantees about
supporting corrupt repos (besides, telling the user that the shelve
doesn't exist when `hg shelve --list` lists it is not very helpful).

Differential Revision: https://phab.mercurial-scm.org/D9698

mercurial/shelve.py

@@ -117,12 +117,7 b' class shelvedfile(object):'
         return self.vfs.stat(self.fname)
 
     def opener(self, mode=b'rb'):
-        try:
-            return self.vfs(self.fname, mode)
-        except IOError as err:
-            if err.errno != errno.ENOENT:
-                raise
-            raise error.Abort(_(b"shelved change '%s' not found") % self.name)
+        return self.vfs(self.fname, mode)
 
     def applybundle(self, tr):
         fp = self.opener()

tests/test-shelve2.t

@@ -756,7 +756,7 b' Test corrupt shelves (in .hg/shelved/, n'
   junk1           (* ago)     (glob)
   $ hg unshelve
   unshelving change 'junk1'
-  abort: shelved change 'junk1' not found
+  abort: $ENOENT$: '$TESTTMP/corrupt-shelves/.hg/shelved/junk1.hg'
   [255]
   $ hg shelve -d junk1
   $ find .hg/shelve* | sort