Exception in greeting function break terminal when inside SVG

[jcubic]

Issue summary

When greeting function throw exception it show stack trace but break --pixel density calculation from #744

Expected behavior

The stack trace is visible with correct pixel-density

Actual behavior

The stack trace is visible but the size is broken.

Steps to reproduce

1. Use devel version with SVG demo and this code

$('#term').terminal($.noop, {
   greetings() {
     dontExist();
   }
});

TODO

• Test all possible functions if exception doesn't break anything else

[jcubic]

Cannot reproduce it anymore