largefiles: don't crash when trying to find default dest for url without path

b32e55e6c3c7 introduced a crash when cloning a url without path - where
util.url().path would be None.

This None will now be handled as ''. clone will thus abort with 'repository /
not found' as before.

mercurial/hg.py

@@ -122,7 +122,7 b' def peer(uiorrepo, opts, path, create=Fa'
 
 def defaultdest(source):
     '''return default destination of clone if none is given'''
-    return os.path.basename(os.path.normpath(util.url(source).path))
+    return os.path.basename(os.path.normpath(util.url(source).path or ''))
 
 def share(ui, source, dest=None, update=True):
     '''create a shared repository'''

tests/test-largefiles.t

@@ -831,6 +831,8 b' Test cloning with --all-largefiles flag'
   commit: (clean)
   update: 8 new changesets (update)
 
+Show computed destination directory:
+
   $ mkdir xyz
   $ cd xyz
   $ hg clone ../a
@@ -841,6 +843,12 b' Test cloning with --all-largefiles flag'
   5 files updated, 0 files merged, 0 files removed, 0 files unresolved
   $ cd ..
 
+Clone URL without path:
+
+  $ hg clone file://
+  abort: repository / not found!
+  [255]
+
 Ensure base clone command argument validation
 
   $ hg clone -U -u 0 a a-clone-failure