`OneOf.options()` emits extra pairs when labels outnumber choices

[T90REAL]

marshmallow.validate.OneOf.options() is supposed to “return the (value, label) pairs, where value is a string associated with each choice.” However the implementation zips choices and labels with zip_longest(..., fillvalue=""), so it produces as many pairs as the longer input. When labels is longer than choices, options() yields phantom entries whose value is the empty string, even though no such choice exists.
Better to raise a ValueErorr?

from marshmallow.validate import OneOf

oneof = OneOf(choices=[], labels=["extra"])
print(list(oneof.options()))
# Expected: []
# Actual: [('', 'extra')]  # bogus option with empty string value

Note: This issue was identified by an automated testing tool for academic research and manually verified. If you have any concerns about this type of reporting, please let me know, and I will adjust my workflow accordingly.

[lafrech]

You're right about the diagnosis.

The fact that the code reads zip_longest(self.choices, self.labels, fillvalue="") makes it look like it was done on purpose but I don't see the reason.

Not sure what to do here. We could raise but this means add a runtime check (although admittedly the perf impact should be small) and this could break people code. A warning might be better until next major version.

(BTW I just fixed the docstring in ba8058a, str() appeared twice due to an overlook in f37ef56.)