Fix error handling in gssint_mechglue_init()

Fix error handling in gssint_mechglue_init()

In the unlikely event that one of the functions called by
gssint_mechglue_init() returns an error, return that error to the
caller rather than continuing on and discarding the error status.
Returning success when some of the operations failed could fool the
library finalizer into thinking that initialization completed.
Reported by Spencer Malone.

ticket: 8864 (new)
tags: pullup
target_version: 1.18
target_version: 1.17-next