Fix 'if (!self.port)' analyze warning (#235)
Fix 'if (!self.port)' analyze warning (#235)

* Fix 'if (!self.port)' analyze warning

Xcode 9 running on macOS High Sierra issues this warning when analyzing with a attached iOS 11.0.1 iPad:

> Pods/NMSSH/NMSSH/NMSSHHostConfig.m:37:10: Converting a pointer value of type 'NSNumber *' to a primitive boolean value; instead, either compare the pointer to nil or call -boolValue

This commit fixes it.

* Compare to nil

As requested in https://github.com/NMSSH/NMSSH/pull/235#discussion_r142046374

eugenehp/NMSSH,Lejdborg/NMSSH,Lejdborg/NMSSH,ADGrant/NMSSH,ricobeck/NMSSH,ricobeck/NMSSH,ADGrant/NMSSH,NMSSH/NMSSH,Lejdborg/NMSSH,ricobeck/NMSSH,eugenehp/NMSSH,NMSSH/NMSSH,Lejdborg/NMSSH,eugenehp/NMSSH,NMSSH/NMSSH,ADGrant/NMSSH,eugenehp/NMSSH