Previously, a PUSHS before a SECTION directive would cause rgbasm to crash when encountering a subsequent POPS.
This is because the subsequently-called out_setCurrentSection() expected the new section to be non-null, which wasn’t the case in this situation. This has been addressed by allowing the ‘null’ section to be set in this function, and only dereferencing it (to set nPC) if a non-null section is to be set.
In practice, this means that PUSHS/POPS can now be used to push/restore a context without a section.
