UI: Port Forwarding form - ports are NULL-ed after canceling chossing Tier/VM.

[andrijapanicsb]

When adding a Port Forwarding rule on Public IP of a VPC, enter private/public port, click ADD to chose Tier and the VM - but then click back/close the VM/Tier-choosing pop-up - the private/public ports fields are deleted.

For comparison, when doing the same on Load Balancing - the fields are not NULL-ed, the entered values for ports still stay as filled in previously.

Short video for simplicity of explanation:

http://somup.com/crfU6ZFUEZ

[yadvr]

cc @shwstppr @davidjumani @Spaceman1984 @Pearl1594

[yadvr]

Fixed in #4981