* Refactor the "s:LoadArgCount()" function
Previously, this function would always set "v:errmsg" on the first
call with a given function. This is because autoloaded functions
are not defined on the first call.
A number of improvements have been made:
- a useless local function ("l:Function") is removed
- the "execute()" builtin captures the output, instead of ":redir"
- a ":try" block handles the case where a function is not defined
- a useless ":if" is removed since ":redir" always defines the var
- confusing quoting is re-written (remove double "'" chars)
Fixes: #3021
8f7ccdc5e9