HPCC-11988 Fix hthor calling helper functions too early

Signed-off-by: Gavin Halliday <gavin.halliday@lexisnexis.com>
serious nit-picking - mix of initializing styles of member variables, here vs e.g.CHThorIndexCountActivity.

Also, it looks like in the master branch, member variables are often initialize in ready() 1st.