bugfix: Empty import combined with real geometry caused an assert failure

src/cgalutils.cc

@@ -94,7 +94,7 @@ namespace CGALUtils {
 			}
 			// Initialize N with first expected geometric object
 			if (!N) {
-				N = chN->copy();;
+				N = chN->copy();
 				continue;
 			}
 
@@ -1106,8 +1106,8 @@ void ZRemover::visit( CGAL_Nef_polyhedron3::Halffacet_const_handle hfacet )
 
 static CGAL_Nef_polyhedron *createNefPolyhedronFromPolySet(const PolySet &ps)
 {
-	assert(ps.getDimension() == 3);
 	if (ps.isEmpty()) return new CGAL_Nef_polyhedron();
+	assert(ps.getDimension() == 3);
 
 	CGAL_Nef_polyhedron3 *N = NULL;
 	bool plane_error = false;

testdata/scad/features/import-empty-tests.scad

@@ -0,0 +1,5 @@
+// Testing that empty imports don't cause problems when mixed with real objects
+difference() {
+  import();
+  cube();
+}

tests/regression/dumptest/import-empty-tests-expected.csg

@@ -0,0 +1,6 @@
+group() {
+	difference() {
+		import(file = "", layer = "", origin = [0, 0], scale = 1, convexity = 1, $fn = 0, $fa = 12, $fs = 2);
+		cube(size = [1, 1, 1], center = false);
+	}
+}