completion: discover repo path in `__git_pseudoref_exists ()`

The helper function `__git_pseudoref_exists ()` expects that the repo
path has already been discovered by its callers, which makes for a
rather fragile calling convention. Refactor the function to discover the
repo path itself to make it more self-contained, which also removes the
need to discover the path in some of its callers.

Signed-off-by: Patrick Steinhardt <ps@pks.im>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

contrib/completion/git-completion.bash

@@ -138,6 +138,8 @@ __git_pseudoref_exists ()
 {
 	local ref=$1
 
+	__git_find_repo_path
+
 	# If the reftable is in use, we have to shell out to 'git rev-parse'
 	# to determine whether the ref exists instead of looking directly in
 	# the filesystem to determine whether the ref exists. Otherwise, use
@@ -1656,7 +1658,6 @@ __git_cherry_pick_inprogress_options=$__git_sequencer_inprogress_options
 
 _git_cherry_pick ()
 {
-	__git_find_repo_path
 	if __git_pseudoref_exists CHERRY_PICK_HEAD; then
 		__gitcomp "$__git_cherry_pick_inprogress_options"
 		return
@@ -2966,7 +2967,6 @@ _git_reset ()
 
 _git_restore ()
 {
-	__git_find_repo_path
 	case "$prev" in
 	-s)
 		__git_complete_refs
@@ -2995,7 +2995,6 @@ __git_revert_inprogress_options=$__git_sequencer_inprogress_options
 
 _git_revert ()
 {
-	__git_find_repo_path
 	if __git_pseudoref_exists REVERT_HEAD; then
 		__gitcomp "$__git_revert_inprogress_options"
 		return