client.c: Modified how client check for proxy informations

The client checks if proxy information is not a "\0" string before getting
it, instead of checking the number of arguments, because they will always
exist.

Signed-off-by: Erik Alexandre Pucci <eap08@c3sl.ufpr.br>
Acked-by: Diego Giovane Pasqualin <dgp06@c3sl.ufpr.br>
Acked-by: Ricardo Tavares de Oliveira <rto07@c3sl.ufpr.br>
Acked-by: Vinicius Ruoso <vkr07@c3sl.ufpr.br>
Signed-off-by: Danilo K. S. Yorinori <danilok@c3sl.ufpr.br>