fix uncaught exception

[frida-161]

My first branch got messed up somehow so here is a new PR. Sorry!

This fixes the uncaught exception in #229

[codecov-commenter]

Codecov Report

Merging #251 (45e42f4) into master (84de3da) will decrease coverage by 18.33%. The diff coverage is 0.00%.

@@            Coverage Diff             @@
##           master    #251       +/-   ##
==========================================
- Coverage   19.12%   0.78%   -18.34%     
==========================================
  Files          42      42               
  Lines        3708    3682       -26     
  Branches      610     555       -55     
==========================================
- Hits          709      29      -680     
- Misses       2947    3652      +705     
+ Partials       52       1       -51     

Impacted Files	Coverage Δ
...lication_schema_toolbox/core/load_gmlas_in_qgis.py	0.00% <0.00%> (-81.72%)	:arrow_down:
...plication_schema_toolbox/gui/import_gmlas_panel.py	0.00% <0.00%> (ø)
..._application_schema_toolbox/gui/load_wizard_wfs.py	0.00% <0.00%> (ø)
gml_application_schema_toolbox/viewers/__init__.py	0.00% <0.00%> (-100.00%)	:arrow_down:
...ml_application_schema_toolbox/toolbelt/__init__.py	0.00% <0.00%> (-100.00%)	:arrow_down:
...l_application_schema_toolbox/gui/custom_viewers.py	0.00% <0.00%> (-90.00%)	:arrow_down:
gml_application_schema_toolbox/core/gmlas_xpath.py	0.00% <0.00%> (-79.32%)	:arrow_down:
...lication_schema_toolbox/gui/wait_cursor_context.py	0.00% <0.00%> (-71.43%)	:arrow_down:
gml_application_schema_toolbox/core/xml_utils.py	0.00% <0.00%> (-68.86%)	:arrow_down:
... and 17 more

[Guts]

Let's catch every exception!

Thanks!