Always true condition in IPAddress string-to-ipv6 conversion

Always true condition in IPAddress string-to-ipv6 conversion

https://github.com/arduino/ArduinoCore-API/blob/master/api/IPAddress.cpp#L204

`*address` is checked to be `':'` so it cannot be `'\0'`. I'm not really sure what the intended behaviour is here.

Read api/IPAddress.cpp around line 204 and inspect the surrounding string-to-IPv6 conversion logic. Determine the intended behavior when the checked character cannot be '\0', then validate the resulting correction against the conversion behavior; the issue is resolved when the condition and its expected behavior are consistent.

Written by the indexing model from the issue text.