Avoid assertion failure in error_message

Avoid assertion failure in error_message

r17942 added a call to get_thread_buffer in the first part of
error_message, prior to the call to com_err_initialize.  This can
cause an assertion failure from k5_getspecific if error_message is
called on a system error before any other com_err functions are
called.  Move the initialization call earlier to prevent this.

(back ported from 6bdaa746fec1cf29adcbe5b8e65c4b8993770b84)

ticket: 8078 (new)
version_fixed: 1.11.6
status: resolved