fix: broken retry loop would break connection management

The retry loop would release connection that would get
re-released upon ``finally`` clause. In consequence, an
exception would be cast.

Signed-off-by: Valentin Lab <valentin.lab@kalysto.org>
Signed-off-by: Nicolas Sebrecht <nicolas.s-dev@laposte.net>

offlineimap/folder/Gmail.py

@@ -72,11 +72,7 @@ class GmailFolder(IMAPFolder):
                   (probably severity MESSAGE) if e.g. no message with
                   this UID could be found.
         """
-        imapobj = self.imapserver.acquireconnection()
-        try:
-            data = self._fetch_from_imap(imapobj, str(uid), 2)
-        finally:
-            self.imapserver.releaseconnection(imapobj)
+        data = self._fetch_from_imap(str(uid), 2)
 
         # data looks now e.g.
         #[('320 (X-GM-LABELS (...) UID 17061 BODY[] {2565}','msgbody....')]