Fix a Swing threading model violation

Hi Dmitry!

I found that SwingTerminalPanel.requestResize() breaks the Swing threading model, by triggering some redraw from outside the EDT.

This is really the same fix than https://github.com/traff/jediterm/commit/1506b25c90c77909ea2f2ec973823db9bc39fc1c

What do you think?

Regards,