ENH: Break out early of loop in argmin/max for bool, fixes #4659

Break out early of loop if the min (max) found is `False` (`True`) when
`argmin` (`argmax`) is called on an array of type `bool`.
Merge pull request #4668 from jaimefrio/fast-argfunc

ENH: Break out early of loop in argmin/max for bool, fixes #4659