[pacman-dev] Do not clobber db if new db is invalid, close a couple "TODO" leaks

[ivy.foster at gmail.com]

Patch 1 is an attempt to close #46107 [1]. In lib/libalpm/be_sync.c,
pacman 1) backs up the old db, 2) procedes as normal, 3) if new db is
valid, deletes backup; if not, restores backup.

While working on patch 1, I noticed a bunch of TODOs that mentioned
the syncpath not being freed or umask reset if pacman ran out of
memory for a MALLOC. Patch 2 fixes them.

[1]: https://bugs.archlinux.org/task/46107?project=3

As always, comments welcome. Enjoy! (-:
Ivy