Fix 500 from account-quota middleware

If a user had set X-Account-Meta-Quota-Bytes to something non-integer
prior to the installation of the account-quota middleware, then the
quota check would choke on it. Now a non-integer value is treated as
"no quota".

Change-Id: I5c38911be1f66fa293aea9c78590d4ce7d184113
Merge "Fix 500 from account-quota middleware"