Currently, in cases where a flag value is required but not passed and
short-option handling is enabled, a panic will occur due to a nil
pointer dereference. This prevents that situation from occurring,
instead propagating the appropriate error.
This makes sorting flags and other sections consistent with how most
command line tools function, by placing both flags `-A` and `-a` before
a flag `-B`.
This will allow users to customize the prefix section or env hint
section of the flag entries in the help menu without having to
reimplement the rest of the logic required in defining FlagStringer.
Robert Liebowitz
