completions/git: Return from the function instead of using a flag

Co-authored-by: Koichi Murase <myoga.murase@gmail.com>

completions/git.completion.bash

@@ -1,7 +1,7 @@
 # bash completion support for Git.
 _omb_completion_git_initialize() {
     if ! _omb_util_function_exists __gitdir; then
-        local is_completion_loaded=0 path
+        local path
         for path in $(type -aP git);
         do
             path="${path%/git}"
@@ -10,15 +10,12 @@ _omb_completion_git_initialize() {
             do
                 local _file="$prefix/$file"
                 if [[ -f $_file && -r $_file ]]; then
-                    is_completion_loaded=1
                     source "$_file"
-                    break 2
+                    return
                 fi
             done
         done
-        if [[ $is_completion_loaded == 0 ]]; then
-            source "$OSH/tools/git-completion.bash"
-        fi
+        source "$OSH/tools/git-completion.bash"
     fi
 }
 _omb_completion_git_initialize