No line for constraint without target

Code notes:

The constraint_has_target can be used to test if a constraint has a target at all.

source/blender/blenkernel/BKE_constraint.h

@@ -55,6 +55,7 @@ void do_constraint_channels (struct ListBase *conbase, struct ListBase *chanbase
 short get_constraint_target (struct bConstraint *con, short ownertype, void *ownerdata, float mat[][4], float size[3], float time);
 struct bConstraintChannel *find_constraint_channel (ListBase *list, const char *name);
 void free_constraint_channels (ListBase *chanbase);
+char constraint_has_target (struct bConstraint *con);
 
 /* Constraint target/owner types */
 #define TARGET_OBJECT			1	//	string is ""

source/blender/blenkernel/intern/constraint.c

@@ -70,6 +70,62 @@ static void constraint_target_to_mat4 (Object *ob, const char *substring, float
 
 /* Functions */
 
+char constraint_has_target (bConstraint *con) {
+	switch (con->type){
+	case CONSTRAINT_TYPE_TRACKTO:
+		{
+			bTrackToConstraint *data = con->data;
+			if (data->tar)
+				return 1;
+		}
+		break;
+	case CONSTRAINT_TYPE_KINEMATIC:
+		{
+			bKinematicConstraint *data = con->data;
+			if (data->tar)
+				return 1;
+		}
+		break;
+	case CONSTRAINT_TYPE_FOLLOWPATH:
+		{
+			bFollowPathConstraint *data = con->data;
+			if (data->tar)
+				return 1;
+		}
+		break;
+	case CONSTRAINT_TYPE_ROTLIKE:
+		{
+			bRotateLikeConstraint *data = con->data;
+			if (data->tar)
+				return 1;
+		}
+		break;
+	case CONSTRAINT_TYPE_LOCLIKE:
+		{
+			bLocateLikeConstraint *data = con->data;
+			if (data->tar)
+				return 1;
+		}
+		break;
+	case CONSTRAINT_TYPE_ACTION:
+		{
+			bActionConstraint *data = con->data;
+			if (data->tar)
+				return 1;
+		}
+		break;
+	case CONSTRAINT_TYPE_LOCKTRACK:
+		{
+			bLockTrackConstraint *data = con->data;
+			if (data->tar)
+				return 1;
+		}
+		break;
+	}
+	// Unknown types or CONSTRAINT_TYPE_NULL or  no target
+	return 0;
+}
+
 void unique_constraint_name (bConstraint *con, ListBase *list){
 	char		tempname[64];
 	int			number;

source/blender/src/drawobject.c

@@ -3716,7 +3716,7 @@ void draw_object(Base *base)
 			glColor3ubv(col2);
 			
 			for (curcon = list->first; curcon; curcon=curcon->next){
-				if ((curcon->flag & CONSTRAINT_EXPAND)&&(curcon->type!=CONSTRAINT_TYPE_NULL)){
+				if ((curcon->flag & CONSTRAINT_EXPAND)&&(curcon->type!=CONSTRAINT_TYPE_NULL)&&(constraint_has_target(curcon))){
 					get_constraint_target(curcon, TARGET_OBJECT, NULL, tmat, size, bsystem_time(ob, 0, (float)(G.scene->r.cfra), ob->sf));
 					setlinestyle(3);
 					glBegin(GL_LINES);

source/blender/src/editconstraint.c

@@ -491,7 +491,10 @@ static short detect_constraint_loop (Object *owner, const char* substring, int d
 				case CONSTRAINT_TYPE_TRACKTO:
 					{
 						bTrackToConstraint *data = curcon->data;
-						if (!exist_object(data->tar)) data->tar = NULL;
+						if (!exist_object(data->tar)) {
+							data->tar = NULL;
+							break;
+						}
 						
 						if (typefrom != CONSTRAINT_TYPE_TRACKTO && typefrom != CONSTRAINT_TYPE_LOCKTRACK){
 							if (add_constraint_element (data->tar, data->subtarget, owner, substring)){