fetch-pack: move fetch initialization

fetch-pack: move fetch initialization

There are some variables initialized at the start of the
do_fetch_pack_v2() state machine. Currently, they are initialized in
FETCH_CHECK_LOCAL, which is the initial state set at the beginning
of the function.

However, a subsequent patch will allow for another initial state,
while still requiring these initialized variables.
Move the initialization to be before the state machine,
so that they are set regardless of the initial state.

Note that there is no change in behavior, because we're moving code
from the beginning of the first state to just before the execution of
the state machine.

Helped-by: Jonathan Tan <redacted>
Helped-by: Christian Couder <redacted>
Signed-off-by: Calvin Wan <redacted>
Signed-off-by: Eric Ju <redacted>
Signed-off-by: Pablo Sabater <redacted>
Signed-off-by: Junio C Hamano <redacted>