Web: terminal renders blank if terminal panel got completely closed

[dbaeumer]

In the Web/UI do the following:

• create a terminal with a pseudo tty
• write to that terminal
• close the terminal

Observe that the whole terminal panel disappears

• create another terminal with a pseudo tty
• Observe: that will recreate the terminal panel.
• write to that terminal

Observe that the terminal doesn't show the text

• create another terminal
• write to it

Observe: the terminal shows the output

• switch back to the terminal created before

Observe: you see the output.

I can provide steps how to reproduce with Python, but I need to merge PRs first and release new npm packages. Let me know if that would help.

[dbaeumer]