[BUG] git completion do sed on binary file

Probably missed since git-merge builtin effort:

__git_merge_strategies ()
{
        if [ -n "$__git_merge_strategylist" ]; then
                echo "$__git_merge_strategylist"
                return
        fi
        sed -n "/^all_strategies='/{
                s/^all_strategies='//
                s/'//
                p
                q
                }" "$(git --exec-path)/git-merge"
}

It takes several seconds to finish that function.