Fix in backend when creating an artificial mainloop (for example in cropper.py).
Fix in backend when creating an artificial mainloop (for example in cropper.py).

pbfy0/visvis,chrisidefix/visvis,Alwnikrotikz/visvis,chrisidefix/visvis,Alwnikrotikz/visvis.dev,Alwnikrotikz/visvis,chrisidefix/visvis,almarklein/visvis.dev,pbfy0/visvis,AlanZatarain/visvis.dev,pbfy0/visvis,chiluf/visvis.dev,Alwnikrotikz/visvis,pbfy0/visvis.dev