PROG: Fixed whitespace and if braces for TableViewContent::showContextMenu. No...

PROG: Fixed whitespace and if braces for TableViewContent::showContextMenu. No functionality has been changed. Fixes issue with misleading-indendation warning occuring during Fedora25 (c++14) builds. Referecnes #4809.

git-svn-id: http://subversion.wr.usgs.gov/repos/prog/isis3/trunk@8154 41f8697f-d340-4b68-9986-7bafba869bb8