qt terminal behavior if no x11 is available

[Dima K. <gn...@di...>]

Hi. Is anybody here familiar with the qt terminal init sequence? I'm
observing that if you try to plot anything without DISPLAY defined, the
qt terminal throws an error and hangs. It does NOT give us the prompt
back. This confuses tools that use gnuplot to make plots.

There was a commit that changed the way this works:

  https://sourceforge.net/p/gnuplot/gnuplot-main/ci/c415285c230

Reverting that makes gnuplot give up after a few seconds. The x11 and
wxt terminals figure it out immediately, but even a wait of several
seconds is better than a forever hang we currently get. Is there a
better way to handle errors in qt?

Thanks!