ref: gl: return NULL in GetEntityByIndex and ModelHandle just in case

ref/gl/gl_local.h

@@ -734,11 +734,17 @@ extern ref_host_t    *gp_host;
 //
 static inline cl_entity_t *CL_GetEntityByIndex( int index )
 {
+	if( unlikely( index < 0 || index >= tr.max_entities || !tr.entities ))
+		return NULL;
+
 	return &tr.entities[index];
 }
 
 static inline model_t *CL_ModelHandle( int index )
 {
+	if( unlikely( index < 0 || index >= gp_cl->nummodels ))
+		return NULL;
+
 	return gp_cl->models[index];
 }