Test that `total_supply` call returns "" vs raise an exception

[rakanalh]

For the comment @hackaugusto made here:

#4936 (comment)

It is assumed that calling total_supply for an invalid token returns "". However, web3 might be throwing an exception.

Acceptance Criteria

• Write a test to verify which case happens
• If an exception is raised, update calls to total_supply to handle the exception.

[palango]

This is the code used in the explorer backend. Maybe that helps: https://github.com/raiden-network/explorer/blob/master/backend/metrics_backend/utils/token.py