[Refactor] Fix for bitflags with only one checked option

Resolves #51.  Using setCurrentIndex on bitflag enums causes the
QComboBox to break when only one option is selected. It returns
something other than -1 and in doing so checked option's UI is inactive.
[Refactor] Fix Qt warning when opening ColorWheel
[Refactor] Prevent UVWidget crash in Debug builds

Did not affect Release builds.  I made the change nonetheless although
I'm not certain it's the best way.  Qt signal/slot is still a bit alien
to me.