[flang][runtime] Don't prematurely end formatted integer input (#76643)

When an input data-list has more items than can be read by a format from
the input record (e.g., "(4I5)" reading "1 2"), don't return false from
EditIntegerInput() just because nothing was read -- that will prevent
later items from being set to zero, as they should be. Return true
unless nothing was read and there is some kind of error pending.

Fixes llvm-error-tests/Fortran/gfortran/regression/pr478478.f90.