Bug when sending tip with default token (eth). tokenAddressToDetails for "0x0" token address returns null.

[dylanjw]

Describe the bug
The issue occurs when sending a tip without clicking the token drop-down and selecting Eth, but instead just letting Eth be the default selection option. In this case, the token address is "0x0" instead of "0x0000000000000000000000000000000000000000". The js function tokenAddressToDetails returns null when the address is 0x0. Javascript console:

> tokenAddressToDetails("0x0");
null
> tokenAddressToDetails("0x0000000000000000000000000000000000000000");
Object { addr: "0x0000000000000000000000000000000000000000", name: "ETH", decimals: 18, priority: 999 }

To Reproduce

I think the real issue is that tokenAddressToDetails returns null. So to reproduce, just run:
tokenAddressToDetails("0x0"); in the console.

Expected behavior
tokenAddressToDetails("0x0"); should return the token details for Eth.

Additional context
I found this issue while working on (#2250) displaying an error message when sending a tip with an insufficient token balance, but there appears to be many places where it looks like `tokenAddressToDetails("0x0"); is assumed to return valid token details.