Help for a fallthrough subcommands does not show upper subcommand help

A help for a subcommand `subc2` does not shown upper level subcommand options. Consider the following structure ``` app subc1 [OPTIONS1] subc2 [OPTIONS2] ``` where subc2 is a subcommand of subc1. The following command will show help message for subcommand 1 (subc1) with the list of `[OPTIONS2]`, but will not include `[OPTIONS1]`. ``` app subc1 subc2 --help ``` `subc2 ` has the fallthrough() flag set. Similar to https://github.com/CLIUtils/CLI11/issues/129