mod_storage_xep0227: treat roster metadata pseudo-entry correctly The roster version is stored in a pseudo-item which has the key `false`. The if condition in the touched code attempts to guard against this, but it does not take into account that the jid prepping returns nil instead of false. By moving the jid prepping into the if, we can check for the metadata entry safely.

The Prosody project is open to contributions (see HACKERS file), but is
maintained daily by:

  - Matthew Wild (mail: matthew [at] prosody.im)
  - Waqas Hussain (mail: waqas [at] prosody.im)
  - Kim Alvefur (mail: zash [at] prosody.im)

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