mq: eliminate warning on qpush with empty series

Warning was "DeprecationWarning: use lock.release instead of del lock"

hgext/mq.py

@@ -902,14 +902,14 b' class queue(object):'
     def push(self, repo, patch=None, force=False, list=False,
              mergeq=None, all=False):
         wlock = repo.wlock()
-        if repo.dirstate.parents()[0] not in repo.heads():
-            self.ui.status(_("(working directory not at a head)\n"))
+        try:
+            if repo.dirstate.parents()[0] not in repo.heads():
+                self.ui.status(_("(working directory not at a head)\n"))
 
-        if not self.series:
-            self.ui.warn(_('no patches in series\n'))
-            return 0
+            if not self.series:
+                self.ui.warn(_('no patches in series\n'))
+                return 0
 
-        try:
             patch = self.lookup(patch)
             # Suppose our series file is: A B C and the current 'top'
             # patch is B. qpush C should be performed (moving forward)

tests/test-mq-qpush-fail

@@ -16,6 +16,10 b" echo 'syntax: glob' > .hgignore"
 echo '.hgignore' >> .hgignore
 
 hg qinit
+
+echo '% test qpush on empty series'
+hg qpush
+
 hg qnew patch1
 echo >> foo
 hg qrefresh -m 'patch 1'

tests/test-mq-qpush-fail.out

@@ -1,4 +1,6 b''
 adding foo
+% test qpush on empty series
+no patches in series
 patch queue now empty
 applying patch1
 applying patch2