Merge branch 'bc/fetch-pack-clear-alternate-shallow'

Merge branch 'bc/fetch-pack-clear-alternate-shallow'

"git fetch" over protocol v2 that needs to make a second connection
to backfill tags did not clear a variable that holds shallow
repository information correctly, leading to an access of freed
piece of memory.

* bc/fetch-pack-clear-alternate-shallow:
  fetch-pack: clear alternate shallow in one more place
  fetch-pack: clear alternate shallow when complete