send-email: minor code refactoring
send-email: minor code refactoring

Group expressions in a single if statement. This avoid checking
multiple time if the variable $sender is defined.

Signed-off-by: Remi Lespinet <22400db3a241109c5f34e07079970b8b4e19596f@ensimag.grenoble-inp.fr>
Signed-off-by: Matthieu Moy <d4d2cc2a6ec7b2aa587d4887cc5ed200f9b685a1@imag.fr>
Signed-off-by: Junio C Hamano <a6723cc3f76163bf7adb636a73ac3b0ceb3e6b9b@pobox.com>

destenson/git,destenson/git,destenson/git,destenson/git,destenson/git,destenson/git,destenson/git,destenson/git