InvalidChar may be confusing in some instances

[nicbus]

The InvalidRString::InvalidChar error contains the character that has been found to be invalid, but it may not match the character in the original string.

As an example, trying to issue an asset using a Unicode character in the ticker or name trigger this issue.

More specifically, issuing a NIA asset with name name with ℧nicode characters throws the error:

string 'name with ℧nicode characters' contains invalid character 'â'

This probably happens because the string is parsed 1 byte at a time and the 1st byte of the Unicode character happens to correspond to the â ASCII character, and this may lead do confusion.

Since the invalid character cannot be correctly interpreted in some cases, it may be better to omit it and just report the string that failed, or report the position of the invalid character in the string (which I think should always be correct) instead of its ASCII representation.