There is no inputting validation for the "port input box"

[v-ruizh]

OS: All
Build Version: 20191221.2
Regression: Not a Regression

Steps to reproduce:

1. Open a folder/workspace in VS Code.
2. F1->Docker: Add Docker Files to Workspace...->Node.js->Yes/No.
3. Input the port with "3;;'['']?><" in the "port input box".

Expect:
There is an error like below.

Actual:
There is no inputting validation for the "port input box".

[allanwright]

I've created #1518 to fix this issue.