Fix issue where right-clicking on an empty space in Heritrix jobs list would cause WAIL to crash.
Fix issue where right-clicking on an empty space in Heritrix jobs
list would cause WAIL to crash.

Closes #430

machawk1/wail,machawk1/wail,machawk1/wail,machawk1/wail,machawk1/wail,machawk1/wail,machawk1/wail,machawk1/wail