Minor optimization at the level of source code for a new ticket by mail.

Hi,

This PR is re-open for below.

https://github.com/OTRS/otrs/pull/208

I'm sorry few my comments.

The codes from line 118 to 125 is sames as from line 95 to 100 in Kernel/System/PostMaster/NewTicket.pm.
And since the value of argument $GetParam{From} is never changed between them.
Therefore, if $GetParam{From} exists, values of $GetParam{EmailFrom} at line 126
and $GetParam{SenderEmailAddress} at line 101 is always equal.

So I set value of $GetParam{EmailFrom} to $GetParam{SenderEmailAddress},
instead of removal of codes from line 118 to 125.

Besides, if $GetParam{From} doesn't exist, %CustomerData is always undef on the codes from line 136 to 156,
because of definition at line 106. So I inserted thire codes into `if ( $GetParam{From} )'.

Could you review this PR again?

Regards,
Norihiro.