Fix animation code accessing invalid sequence descriptor.

https://github.com/ValveSoftware/halflife/issues/3308

dlls/animation.cpp

@@ -238,7 +238,7 @@ void GetSequenceInfo( void *pmodel, entvars_t *pev, float *pflFrameRate, float *
 
 	mstudioseqdesc_t *pseqdesc;
 
-	if( pev->sequence >= pstudiohdr->numseq )
+	if( pev->sequence < 0 || pev->sequence >= pstudiohdr->numseq )
 	{
 		*pflFrameRate = 0.0f;
 		*pflGroundSpeed = 0.0f;
@@ -265,7 +265,7 @@ int GetSequenceFlags( void *pmodel, entvars_t *pev )
 	studiohdr_t *pstudiohdr;
 
 	pstudiohdr = (studiohdr_t *)pmodel;
-	if( !pstudiohdr || pev->sequence >= pstudiohdr->numseq )
+	if( !pstudiohdr || pev->sequence < 0 || pev->sequence >= pstudiohdr->numseq )
 		return 0;
 
 	mstudioseqdesc_t *pseqdesc;
@@ -279,7 +279,7 @@ int GetAnimationEvent( void *pmodel, entvars_t *pev, MonsterEvent_t *pMonsterEve
 	studiohdr_t *pstudiohdr;
 
 	pstudiohdr = (studiohdr_t *)pmodel;
-	if( !pstudiohdr || pev->sequence >= pstudiohdr->numseq || !pMonsterEvent )
+	if( !pstudiohdr || pev->sequence < 0 || pev->sequence >= pstudiohdr->numseq || !pMonsterEvent )
 		return 0;
 
 	mstudioseqdesc_t *pseqdesc;
@@ -379,7 +379,7 @@ float SetBlending( void *pmodel, entvars_t *pev, int iBlender, float flValue )
 	studiohdr_t *pstudiohdr;
 
 	pstudiohdr = (studiohdr_t *)pmodel;
-	if( !pstudiohdr )
+	if( !pstudiohdr || pev->sequence < 0 || pev->sequence >= pstudiohdr->numseq )
 		return flValue;
 
 	mstudioseqdesc_t *pseqdesc;