fix(mobile): items not deselecting on back button

[YarosMallorca]

Description

Fixed back-button logic on asset grid.
Before, when items were selected, upon pressing the back button, they wouldn't deselect. This fixes that behavior.

How Has This Been Tested?

• Select one or more items on the main grid, trash, or in an album, then press the back button - it will deselect the items, but not pop the route
• Go to an album, and press "add photos", on the next screen, select a couple of photos to add, but then press the back button, the selected photos will deselect themselves (but the ones that were preselected will stay). If only preselected are currently selected, it will pop the route.

Video demo

back-button-fix.mp4

What's left to fix?

On the search results page, it still doesn't prevent the route from popping when assets are selected.
I cannot figure out why on the search results page, the _selectedAssets in ImmichAssetGridView is always empty. If someone could take a look at that or point me in the right direction, I would highly appreciate it :)

[shenlong-tanwen]

The Search page seems to be acting weird. The first pass to the PopScope are the default values, so selectionActive - false and selectedAssets - empty and so the pop actually happens. However, the onPopInvokedWithResult callback is called again, this time with the proper value, but by this time the Route already pops off.

Commenting out the else part to prevent and pressing the back button puts the timeline in a weird state as well. Probably worth investigating separately.