fix a crash in splash:wait_for_resume

[kmike]

It looks like recent PyQT versions exit the process if a Python function called from JS raises an exception.

[codecov]

Codecov Report

Merging #879 into master will decrease coverage by 1.41%.
The diff coverage is 100%.

@@            Coverage Diff             @@
##           master     #879      +/-   ##
==========================================
- Coverage   89.08%   87.67%   -1.42%     
==========================================
  Files          41       41              
  Lines        5725     5726       +1     
  Branches      791      791              
==========================================
- Hits         5100     5020      -80     
- Misses        452      525      +73     
- Partials      173      181       +8

Impacted Files	Coverage Δ
splash/exceptions.py	100% <ø> (ø)	⬆️
splash/browser_tab.py	93.16% <100%> (-0.77%)	⬇️
splash/kernel/__main__.py	0% <0%> (-66.67%)	⬇️
splash/kernel/kernelbase.py	20.58% <0%> (-27.95%)	⬇️
splash/kernel/kernel.py	33.33% <0%> (-20.41%)	⬇️
splash/kernel/completer.py	88.31% <0%> (-7.8%)	⬇️
splash/server.py	75% <0%> (-5.44%)	⬇️
splash/qtutils.py	79.73% <0%> (-1.97%)	⬇️
splash/network_manager.py	84.33% <0%> (-0.34%)	⬇️
... and 1 more