tryparse should still throw an exception on invalid base

[stevengj]

tryparse does not throw an exception on an invalid string, but it should still throw an ArgumentError if the base argument is invalid. This fixes a regression apparently introduced by #17078.

In particular, this regression has broken the Compat.jl tests (see e.g. JuliaLang/Compat.jl#245, JuliaLang/Compat.jl#240).

cc: @yuyichao, @quinnj

[stevengj]

Oh grr, we need to distinguish the base passed by the user (which should throw) from the base extracted by parseint_preamble (which shouldn't throw).

[stevengj]

Okay, should be fixed now, I hope.

[stevengj]

AppVeyor failure in pkg test seems to be an unrelated network problem: GitError(Code:ERROR, Class:OS, Failed to receive response: The server returned an invalid or unrecognized response).

[quinnj]

LGTM