#24 Fix build with clang 6

[Craig Leres]

Here's a patch that unbreaks building on FreeBSD 11.2-RELEASE with clang 6.0.0:

jtagrw.cc:134:13: error: cannot initialize return object of type 'uchar *' (aka 'unsigned char *') with an rvalue of type 'bool'
            return false;
                   ^~~~~

[Craig Leres]

Patch

[Joerg Wunsch]

This has been replaced by throwing an exception.