Import filename lost on windows

[Nicholas Devenish]

• Import some images
• Close DUI
• Reopen DUI

Cause is

DUI/src/dui/custom_widgets.py

Lines 494 to 496 in 49d4923

 if singl_com[0:1] == "/": 
     self.path_file_str = str(singl_com) 
     self.put_str_lin() 

- ignoring anything that isn't a beam centre, inversion or /-starting path.