autoname: Check for potential overflow

[KrystalDelusion]

What are the reasons/motivation for this change?
Fix #4983
While unlikely, a wire with a score greater than about INT32_MAX/20000 will lead to an interger overflow when trying to rename users of that wire.

Explain how this is achieved.
Call log_error if any of the wires have a score over INT32_MAX/24000. Because the score is calculated with (10000*score + new_name.size())*2, if the new name is longer than 2000 characters long then there could still be an integer overflow, but this seems sufficiently unlikely that I thought checking each wire score once was better than checking each proposal, while still allowing for a fanout of almost 90000 bits from a single wire.

If applicable, please suggest to reviewers how they can test the change.