[flang][runtime] INQUIRE(UNIT=666,NUMBER=n) must set n=666

Whether a unit number in an inquire-by-unit statement is valid or not,
it should be the value to which the NUMBER= variable is set, not -1.
-1 should be returned to NUMBER= only for an inquire-by-file statement
when the FILE= is not connected to any unit.

Differential Revision: https://reviews.llvm.org/D126145