Fix portals

• Resetting portalcullsector fixes the major visual glitches
• Using 32 bits for nummasks and i fixes crashes when rendering lots of portals

Test build: (based on next so be careful with your save files)

srb2win_fix-portals.exe

One map for testing portals: (breaks without this patch)

bigportals.wad (it's just the portal example map from the wiki, but stretched)