Fixes

• Only sync on a fully validated vblanking interval (i.e. top vblank, hsync lines, bottom vblank, should have the expected distances before syncing, otherwise, use the estimated sync position)
  • Fixes edge case where damaged VHS (not fallback-vsync) causes either the first or second vblank to improperly be detected and the sync to jump.
• Only change field order if syncing on validated vblanking interval; otherwise, use opposite of previous frame.
  • Prevents duplicate field orders from being detected when vblanking area is damaged