pad.c:pad_free: Don’t reset PL_padix if using pad_reset

pad.c:pad_free: Don’t reset PL_padix if using pad_reset

pad_reset causes PL_padix to be reset at the beginning of each state-
ment, so that operator targets can be reused.

If we also reset it when freeing an operator, then theoretically tar-
gets from operators later on in the same statement might be reused.  I
can’t come up with a test case, but it’s better to be safe than sorry.