Fix parser crash bug exposed by wild tests.

This was caused by the main_loop refactoring.

Example of file that was crashing, and now parses:

illumos-gate/usr/src/lib/libshell/common/tests/expand.sh

osh/cmd_parse.py

@@ -1486,6 +1486,10 @@ def _ParseCommandLine(self):
       b. If there's a sync_op, process it.  Then look for a newline and
          return.  Otherwise, parse another AndOr.
    """
    # NOTE: This is slightly different than END_LIST in _ParseCommandTerm, and
    # unfortunately somewhat ad hoc.
    END_LIST = (Id.Op_Newline, Id.Eof_Real, Id.Op_RParen)

    children = []
    done = False
    while not done:
@@ -1498,13 +1502,10 @@ def _ParseCommandLine(self):
        self._Next()

        self._Peek()
        if self.c_id in (Id.Op_Newline, Id.Eof_Real):
        if self.c_id in END_LIST:
          done = True

      elif self.c_id == Id.Op_Newline:
        done = True

      elif self.c_id == Id.Eof_Real:
      elif self.c_id in END_LIST:
        done = True

      else: