smr_file_create.php: fix MGU compatibility
smr_file_create.php: fix MGU compatibility

MGU needs the first comment line to start with `;SMR1.6`.
Add that back in so that MGU can load sector files again.

smrealms/smr,hemberger/smr,smrealms/smr,hemberger/smr,hemberger/smr,smrealms/smr,hemberger/smr