fix winrmpass sanitization to account for empty string value.
fix winrmpass sanitization to account for empty string value.

mitchellh/packer,dave2/packer,grubernaut/packer,hashicorp/packer,paulmey/packer,dave2/packer,rnaveiras/packer,pecigonzalo/packer,mitchellh/packer,dave2/packer,hashicorp/packer,ricardclau/packer,rnaveiras/packer,grubernaut/packer,grubernaut/packer,grubernaut/packer,ricardclau/packer,hashicorp/packer,dave2/packer,grubernaut/packer,mitchellh/packer,pecigonzalo/packer,pecigonzalo/packer,mitchellh/packer,rnaveiras/packer,paulmey/packer,ricardclau/packer,dave2/packer,paulmey/packer,rnaveiras/packer,ricardclau/packer,paulmey/packer,dave2/packer,mitchellh/packer,grubernaut/packer,paulmey/packer,ricardclau/packer,ricardclau/packer,rnaveiras/packer,rnaveiras/packer,paulmey/packer,hashicorp/packer,pecigonzalo/packer