Missing position data kills the app with os.Exit(1) and no useful information

[senorprogrammer]

The following two formats for invalid position data cause the app to die with no useful debugging information:

position:
top: 1
left: 1
width: 1
height: 1

and

# position:
    # top: 1
    # left: 1
    # width: 1
    # height: 1

In both cases useful debugging information should be provided.

[senorprogrammer]

Closed by #489