title: No PreValidation stage when converting email to case
body: <p>I have a plugin triggering <em>pre-validation</em> of <em>create incident</em> to assign ticketnumber before the built-in numbering does that. It works like a charm.</p>
  
  <p>But when I have an email and use the <strong>Convert to Case</strong> button, <em>pre-validation</em> never triggers. I can only get plugins to fire on <em>pre-operation</em>, where the ticketnumber is already assigned.</p>
  
  <p>Anyone know how to get around that? Is there another message to look for? Or is the only way to change my plugin to "detect" if the oob numbering has kicked in and let it fire on pre-operation?</p>
  
  <p>And is there no pre-validation stage available for cases created from email?</p>
  
  <p>(of course I could have my plugin always assign my own numbers, but it is a generic plugin that can be used for any entity and is designed to be unobtrusive, and I would like to keep it that way. I would also prefer it to run pre-operation, but oob numbering strikes at the <em>internal pre-operation</em> stage)</p>