[flang] Remove typo that affected complex namelist input

A recent patch to real/complex formatted input included what must
have been an editing hiccup: "++ ++p" instead of "++p".  This
compiles, and it broke the consumption of the trailing ')' of a
complex value in namelist input by skipping over the character.

Extend existing test to cover this case.

Differential Revision: https://reviews.llvm.org/D114297