fix: make sure the initialization to throw an exception when there is no match url

[nikli2009]

A minor checking added to network initialization.

Context

Found this when launching Uniswap interface locally and chose the Evmos chain. The original error I got is :

So I looked into it a bit and seems we have a assumption that urls will not be empty which in fact it could be.

and 🤔 I reckon there is something we could do about it like :

• Exit early when conditions check fails
• Make sure the user of web3-react can capture this Unhandled Rejection with a more meaningful error name.

Plz let me know if this makes sense to you :D

Changes

• Add additional urls null check.
• Add unit test for the edge case.