bug: newly created tokens with `synced: true` and no holders

[lucasmenendez]

Sometimes (almost all of them in stage) the newly created tokens have the synced attribute set to true and have not yet been scanned (they have no holders).

Example: https://census3-stg.vocdoni.net/api/tokens/0xDD022bE0A7CA78ce7F71d63fb5010D9323A0C7cf?chainID=80001

[lucasmenendez]

Update:

We detect another edge case: if the creation block is newer than the last network block cached in census3, the scanner returns that the tokens is synced without scan any log, because it reach that last network block doing nothing.