subrepo: ensure "lock.release()" execution at the end of "storeclean()"

Before this patch, "lock.release()" for "self._repo" in "storeclean()"
of "hgsubrepo" may not be executed, if unexpected exception is raised,
because it isn't executed in "finally" clause.

This patch ensures "lock.release()" execution at the end of
"storeclean()" by moving it into "finally" clause.

This patch chooses moving almost all lines in "storeclean()" into
"_storeclean()" instead of indenting them for "try/finally" clauses,
to keep diff simple for review-ability.

mercurial/subrepo.py

@@ -525,8 +525,14 b' class hgsubrepo(abstractsubrepo):'
         self._initrepo(r, state[0], create)
 
     def storeclean(self, path):
+        lock = self._repo.lock()
+        try:
+            return self._storeclean(path)
+        finally:
+            lock.release()
+
+    def _storeclean(self, path):
         clean = True
-        lock = self._repo.lock()
         itercache = self._calcstorehash(path)
         try:
             for filehash in self._readstorehashcache(path):
@@ -543,7 +549,6 b' class hgsubrepo(abstractsubrepo):'
                 clean = False
             except StopIteration:
                 pass
-        lock.release()
         return clean
 
     def _calcstorehash(self, remotepath):