fix: prevent asset to buy dropdown from opening if asset to buy is already set

[derHowie]

Fixes BX-1612

What changed (plus any additional context for devs)

We are not focusing the asset to buy dropdown on the swap screen if asset to buy is already set.

Screen recordings / screenshots

PoW: https://www.loom.com/share/4c0b1883a5b84c76a2cc1e798b8d761b

What to test

Ensure the dropdown remains closed when navigating to the swap screen with an asset to buy already set.

[linear[bot]]

BX-1612 Default token output selection fails to dismiss token selector