shelve: fix crash on unshelve without .shelve metadata file

Follow up for c67c94c0e7ae and 38373da1af02.

The inline comment says "we should keep track of the unshelve node in case
we need to reuse it." Perhaps such case isn't tested, and this patch does
NOT add a test for the reuse of the unbundled revision.

Also, I have no idea what should be done if new revision is unbundled
because of "node not in repo".

hgext/shelve.py

@@ -765,6 +765,7 b' def _commitworkingcopychanges(ui, repo, '
 def _unshelverestorecommit(ui, repo, basename):
     """Recreate commit in the repository during the unshelve"""
     repo = repo.unfiltered()
+    node = None
     if shelvedfile(repo, basename, 'shelve').exists():
         node = shelvedfile(repo, basename, 'shelve').readinfo()['node']
     if node is None or node not in repo:
@@ -774,7 +775,7 b' def _unshelverestorecommit(ui, repo, bas'
         # We might not strip the unbundled changeset, so we should keep track of
         # the unshelve node in case we need to reuse it (eg: unshelve --keep)
         if node is None:
-            info = {'node': nodemod.hex(node)}
+            info = {'node': nodemod.hex(shelvectx.node())}
             shelvedfile(repo, basename, 'shelve').writeinfo(info)
     else:
         shelvectx = repo[node]

tests/test-shelve.t

@@ -1793,5 +1793,23 b' putting v1 shelvedstate file in place of'
 mercurial does not crash
   $ hg unshelve --continue
   unshelve of 'ashelve' complete
+
+Unshelve without .shelve metadata:
+
+  $ hg shelve
+  shelved as default
+  1 files updated, 0 files merged, 0 files removed, 0 files unresolved
+  $ rm .hg/shelved/default.shelve
+  $ echo 3 > a
+  $ hg unshelve
+  unshelving change 'default'
+  temporarily committing pending changes (restore with 'hg unshelve --abort')
+  rebasing shelved changes
+  merging a
+  warning: conflicts while merging a! (edit, then use 'hg resolve --mark')
+  unresolved conflicts (see 'hg resolve', then 'hg unshelve --continue')
+  [1]
+  $ cat .hg/shelved/default.shelve
+  node=82e0cb9893247d12667017593ce1e5655860f1ac
+
   $ cd ..
-