Fix crash with libgit when it's compiled with GIT_THREADS

Call git_threads_init() before using libgit functions.

The documentation says:

"If libgit2 has been built with GIT_THREADS on, this function must
 be called once before any other library functions.

 If libgit2 has been built without GIT_THREADS support, this function
 is a no-op"

Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
Signed-off-by: Dirk Hohndel <dirk@hohndel.org>