Draw manager: Don't check matrix to be non-NULL

It isn't a pointer, so the check was confusing and totally redundant.

source/blender/draw/intern/draw_manager.c

@@ -1788,7 +1788,7 @@ static void draw_shgroup(DRWShadingGroup *shgroup, DRWState pass_state)
 	}
 	else {
 		for (DRWCall *call = shgroup->calls.first; call; call = call->head.next) {
-			bool neg_scale = call->obmat && is_negative_m4(call->obmat);
+			bool neg_scale = is_negative_m4(call->obmat);
 
 			/* Negative scale objects */
 			if (neg_scale) {