CRM-14386 fix for : form rule validation notifications not shown

Reproducible by following : Visit New Individual screen and without filling any details, save the form, the expected validation notification for 'email or first name and last name are required' doesn't appear.

The bug : somehow assigned value for <code>$snippet = 0 </code> fails this :  <code> $snippet neq 'json' </code>  check.

The fix : verified the numeric values and noticed this only happens for snippet = 0 value, so made some minor modifications to the condition.