macosx: Fix crash when going forwards after having gone backwards in browse view

When generating new input item node child nodes upon entering a new input node, we deleting the previous instances of the child nodes. This left dangling references in the navigation stack's nav states, leading to crashing when going forwards more than once after having gone backwards using the toolbar buttons

To fix this we now check which stored navigation states are going to be affected by the child node deletion process and provide them with new input node instances which are valid

Signed-off-by: Claudio Cambra developer@claudiocambra.com