Canceling main widget causes error

[Fabian Thiel]

An error has occurred while executing Python code: 

AttributeError: 'Widget' object has no attribute 'task' 
Traceback (most recent call last):
  File "C:/Users/thielf54/AppData/Roaming/QGIS/QGIS3\profiles\default/python/plugins\force4qgis\force4qgis\widget.py", line 176, in onCancelClicked
    self.task.cancel()
AttributeError: 'Widget' object has no attribute 'task'


Python version: 3.7.0 (v3.7.0:1bf9cc5093, Jun 27 2018, 04:59:51) [MSC v.1914 64 bit (AMD64)] 
QGIS version: 3.16.0-Hannover Hannover, 43b64b13f3 

‌

[Andreas Janz]

resolves #25

→ <<cset 45f9e73ac947>>