Back button resets ship browser after making first new fit for a hull

[dsharhon]

Bug Report

Expected behavior:

When you're in a list of fits for a hull, the back button (<<) should go back to the list of hulls for the current ship class.

Actual behavior:

If you've just made the first fit for this hull, the back button acts like the reset button (|<) and goes all the way back to the root list of ship classes. This is annoying when you're making a bunch of new fits to compare hulls in the same class.

Detailed steps to reproduce:

If you have no fits for the "Retribution" hull, as an example:

1. Launch program
2. Click "Assault Frigate"
3. Click "Retribution"
4. Click checkmark button
5. Click back button
   The navigation pane location should now be the list of "Assault Frigate" hull types ("Retribution", "Vengeance", "Harpy"...), but is instead the list of ship classes ("Assault Frigate", "Attack Battlecruiser", "Battleship"...)

Release or development git branch? Please note the release version or commit hash:

Release

Operating system and version (eg: Windows 10, OS X 10.9, OS X 10.11, Ubuntu 16.10):

Windows 10