PythonVideoAnnotator crashes when right-clicking the left pane after removing all videos/objects from the list.

[miguelgaspar24]

Bug description
PythonVideoAnnotator crashes when right-clicking the left pane after removing all videos/objects from the list.

To Reproduce

1. Load a project or open a video.

2. Remove all added videos/project objects.

3. Right-click the now empty pane.

Output error trace:

Traceback (most recent call last):
  File "c:\users\miguel gaspar\desktop\my_virtual_environments\video_annotator\lib\site-packages\pyforms_gui\controls\control_tree.py", line 262, in about_to_show_contextmenu_event
    itemSelected = self.selectedItems()[0]
IndexError: list index out of range

Expected behavior
The expectation would be for the program to not crash, or that right-clicking would open a window with the option to load videos/opening a projecting, similarly to clicking the respective buttons.

Desktop and Versioning Details

OS: Microsoft Windows 10 Pro x64

Virtual Environment Python: 3.6.2

Python Video Annotator and Modules:

Python-video-annotator                                 3.306
Python-video-annotator-models                          0.8.82
Python-video-annotator-models-gui                      0.7.63
Python-video-annotator-module-background-finder        0.5.21
Python-video-annotator-module-contours-images          0.5.28
Python-video-annotator-module-create-paths             0.5.15
Python-video-annotator-module-deeplab                  0.902.21
Python-video-annotator-module-distances                0.5.18
Python-video-annotator-module-eventstats               0.5.15
Python-video-annotator-module-find-orientation         0.5.18
Python-video-annotator-module-import-export            0.5.23
Python-video-annotator-module-motion-counter           0.5.26
Python-video-annotator-module-path-editor              0.5.28
Python-video-annotator-module-path-map                 0.6.16
Python-video-annotator-module-regions-filter           0.5.18
Python-video-annotator-module-smooth-paths             0.5.19
Python-video-annotator-module-timeline                 0.6.26
Python-video-annotator-module-tracking                 0.6.38
Python-video-annotator-module-virtual-object-generator 0.6.26