In qmos, fixed a bug that caused qmos to sometimes freeze, in the grid tool,...

In qmos, fixed a bug that caused qmos to sometimes freeze, in the grid tool, when the maximum longitude was set to a negative value. Fixes #1060.

git-svn-id: http://subversion.wr.usgs.gov/repos/prog/isis3/trunk@4993 41f8697f-d340-4b68-9986-7bafba869bb8