Fix segfault trying to create IfcSweptDiskSolid with invalid curve #5474

In my case it was IfcIndexedPolyCurve with just 1 vertex. Though kernel->convert does return a boolean value to indicate if conversion was successful, we never used it - so it failed silently leading to segfault later on.
Now we also stop processing those polycurves during mapping stage but checking kernel->convert result still might be useful in some other cases.

src/ifcgeom/kernels/opencascade/loop.cpp

@@ -95,8 +95,10 @@ namespace {
 
 		OpenCascadeKernel::curve_creation_visitor_result_type operator()(const taxonomy::loop::ptr& l) {
 			TopoDS_Wire wire;
-			kernel->convert(l, wire);
-			return result = wire;
+			if (!kernel->convert(l, wire)) {
+				throw std::runtime_error("Failed to convert loop to wire");
+			}
+			return result;
 		}
 
 		OpenCascadeKernel::curve_creation_visitor_result_type operator()(const taxonomy::edge::ptr& e) {