[BUG] lock map when change nextmod1v1 to another match

[apples1949]

Describe the bug
When someone plays the nextmod 1v1 configuration and passes 1-2 levels normally, switch to another configuration. The level switched upon passing is the original third level.

To Reproduce
Steps to reproduce the behavior:

1. Switch to the nextmod1v1 map c1m1_hotel
2. Normally pass through two levels
3. Switch to another configuration
4. After normally completing the level, the map is switched to c1m3_mall

Screenshots/Video
none

Server Operating System (if applicable):

• Linux

Additional context
Temporary solution: In confogl_off.cfg, add the following: sm_nextmap ""
Plugins that may trigger the issue: l4d2_map_transitions