Prevent wallet from randomly crashing when current network is Arbitrum

[onyb]

If the currently selected network is one that does not support Buy and Swap, relaunching the browser will make the wallet crash with a blank page. The following error is seen in the terminal logs / console:

[44944:259:0215/210451.230463:ERROR:CONSOLE(57318)] "Uncaught TypeError: Cannot read properties of undefined (reading 'decimals')", source: chrome://wallet/brave_wallet_page.bundle.js (57318)
[44944:259:0215/210451.233778:ERROR:CONSOLE(234637)] "The above error occurred in the <Send> component:
    in Send (created by SendTab)
    in SendTab (created by BuySendSwap)
    in div (created by MainContainer)
    in MainContainer (created by BuySendSwapLayout)
    in div (created by MainContainerWrapper)
    in MainContainerWrapper (created by BuySendSwapLayout)
    in div (created by StyledWrapper)
    in StyledWrapper (created by BuySendSwapLayout)
    in BuySendSwapLayout (created by BuySendSwap)
    in BuySendSwap (created by Container)
    in div (created by WalletWidgetStandIn)
    in WalletWidgetStandIn (created by Container)
    in div (created by StyledContent)
    in StyledContent (created by wallet_page_layout_WalletPageLayout)
    in div (created by StyledWrapper)
    in StyledWrapper (created by wallet_page_layout_WalletPageLayout)
    in wallet_page_layout_WalletPageLayout (created by Container)
    in Container (created by ConnectFunction)
    in ConnectFunction (created by App)
    in Le (created by BraveCoreThemeProvider_BraveCoreThemeProvider)
    in BraveCoreThemeProvider_BraveCoreThemeProvider (created by App)
    in Router (created by BrowserRouter)
    in BrowserRouter (created by App)
    in Provider (created by App)
    in App

Consider adding an error boundary to your tree to customize error handling behavior.
Visit https://fb.me/react-error-boundaries to learn more about error boundaries.", source: chrome://wallet/brave_wallet_page.bundle.js (234637)
[44944:259:0215/210451.241858:ERROR:CONSOLE(57318)] "Uncaught (in promise) TypeError: Cannot read properties of undefined (reading 'decimals')", source: chrome://wallet/brave_wallet_page.bundle.js (57318)

To reproduce:

1. Add Arbitrum network from chainlist.org.
2. Switch to Arbitrum.
3. Relaunch the browser.
4. Wallet page should crash with a blank screen.

⚠️ The issue is not always reproducible easily.

[Uni-verse]

Verified crashing fix using

Brave	1.37.105 Chromium: 100.0.4896.46 (Official Build) (x86_64)
Revision	5ca33821b2211805855c77d334353d27c616a7ca-refs/branch-heads/4896@{#584}
OS	macOS Version 12.1 (Build 21C52)

• Verified not able to reproduce crash. Tried Arbitrum One, BSC, Moonriver, Cronos chains.

STR:

1. Add Arbitrum network from chainlist.org.
2. Switch to Arbitrum.
3. Relaunch the browser.
4. Wallet page should crash with a blank screen.