initialize members of struct to avoid problems with serialisation

This PR fixes a problem in the serialisatoin unit test seen in the CLANG builds, where a 
non-initialised boolean variable causing problems as it's value was -1 (oxff) while the 
C++ standard allows only 0 (false) and 1 (true), and the serialisation code (the EOS 
portable binary archive) expects only the standard values.