Bug: Prototype check in mset command can crash the game
Danger: High - Will crash if a PLR flag has the same value as an ACT flag and is edited on a PC.
Found by: Qidexan
Fixed by: Qidexan/Samson

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build.c, do_mset

In the "flags" section, locate:

      if( IS_SET( victim->act, ACT_PROTOTYPE ) )
         protoflag = TRUE;

Change to:

      if( IS_NPC( victim ) && IS_SET( victim->act, ACT_PROTOTYPE ) )
         protoflag = TRUE;

Locate:

      if( IS_SET( victim->act, ACT_PROTOTYPE ) || ( value == ACT_PROTOTYPE && protoflag ) )
         victim->pIndexData->act = victim->act;

Change to:

      if( IS_NPC( victim ) && ( IS_SET( victim->act, ACT_PROTOTYPE ) || ( 1 << value == ACT_PROTOTYPE && protoflag ) ) )
         victim->pIndexData->act = victim->act;

The prototype checking in this function is not verifying that the victim is an NPC. While the first check would remain relatively harmless, the second one will result in a crash if the PC being edited happens to have the PLR flag with the same numerical value set.