Merge branch 'ab/refspec-init-fix'

Make refspec parsing codepath more robust.

* ab/refspec-init-fix:
refspec: initalize `refspec_item` in `valid_fetch_refspec()`
refspec: add back a refspec_item_init() function
refspec: s/refspec_item_init/&_or_die/g

diff --cc builtin/clone.c
Simple merge

diff --cc builtin/pull.c
Simple merge

diff --cc refspec.c
Simple merge