[QA] Quota fields with parse errors should not be used

[jnweiger]

Seen in user_ldap 0.15.3-rc1 with core 10.8.0-beta1

In ldap, I specified 12x5 B as a user's quota value. This is a broken syntax. but it is accepted into ownCloud

Expected behaviour: It should be rejected. Fallback to ldap default quota or fallback to owncloud default quota.