validateByteRange: correctly handle bytes > 127
validateByteRange: correctly handle bytes > 127

ValidateByteRange::evaluate compared bytes with values in
range [0-255], but acquired bytes by indexing std::string,
which gave type char, which is signed. So bytes with values
more than 127 were treated as negative, resulting in being
incorrectly classified as out-of-range. This commit adds
casting byte values to unsigned char before validating range.

defanator/ModSecurity,defanator/ModSecurity,defanator/ModSecurity,SpiderLabs/ModSecurity,SpiderLabs/ModSecurity,SpiderLabs/ModSecurity