Pancake parser fails with comment after final return

[Kswin01]

Currently, if there are any comments placed after the final return statement, a parser error is thrown. Not the most obvious parser error to find. @mn200.

[IlmariReissumies]

During discussions today, we found that this only happens when the comment line lacks a newline at the end. The culprit is skip_comment_def from the Pancake lexer theory, so it's hopefully an easy fix.