Discover assets loading indicator is not removed

[StephenHeaps]

Description:

A certain case can cause the loading spinner shown on Portfolio when discovering assets is not removed correctly.

Steps to Reproduce

1. Unlock your wallet
2. Wait for loading spinner beside Assets header to disappear
3. Lock your wallet & immediately unlock it again
4. Observe loading spinner never stops until scrolling

Actual result:

Simulator.Screen.Recording.-.iPhone.14.Pro.-.2023-05-10.at.17.17.37.mp4

Expected result:

Loading indicator is eventually removed after discovery completes

Reproduces how often: [Easily reproduced, Intermittent Issue]

Brave Version:

• Can you reproduce this issue with the most recent build from TestFlight?
• Can you reproduce this issue with the previous version of the current build from TestFlight?
• Can you reproduce this issue with the current build from AppStore?

Device details:

Website problems only:

• did you check with Brave Shields down?
• did you check in Safari/Firefox (WkWebView-based browsers)?

Additional Information

[srirambv]

Verification passed on the following devices running 1.52 (23.6.1.16)

• Verified steps from #7434
• Verified asset loading indicator is not shown every time wallet is locked and unlocked

iPhone 7+ (iOS 15.4.8)	iPhone 13 (iOS 16.5)	iPad Pro (iOS 16.6 Beta)
7433-iPhone.7+.MP4	7433-iPhone.13.MP4	7433-iPad.Pro.MP4