subrepo: ensure "close()" execution at the end of "_cachestorehash()"

Before this patch, "close()" for the file object opened in
"_cachestorehash()" may not be executed, if unexpected exception is
raised, because it isn't executed in "finally" clause.

This patch ensures "close()" execution at the end of
"_cachestorehash()" by moving it into "finally" clause.

mercurial/subrepo.py

@@ -596,8 +596,10 b' class hgsubrepo(abstractsubrepo):'
             if not os.path.exists(cachedir):
                 util.makedirs(cachedir, notindexed=True)
             fd = open(cachefile, 'w')
-            fd.writelines(storehash)
-            fd.close()
+            try:
+                fd.writelines(storehash)
+            finally:
+                fd.close()
         finally:
             lock.release()