Send email from contact or find contacts screen wrongly autocompletes

When you select the option to send an email to a contact, the autocomplete returns the email of the current user rather than the selected contact. This happens in CRM/Contact/Form/Task/Email.php when it tries to use the variable $cid to set display name in the title. I added an if/else statement but it could also be removed entirely. It also fixes the issue which sets the title of the new email page as "- Email".