Try to auto-fix any invalid generated helix

src/Mod/PartDesign/App/FeatureHelix.cpp

@@ -36,6 +36,7 @@
 # include <BRepOffsetAPI_MakePipeShell.hxx>
 # include <BRepPrimAPI_MakeRevol.hxx>
 # include <ShapeFix_ShapeTolerance.hxx>
+# include <ShapeFix_Solid.hxx>
 # include <Precision.hxx>
 # include <TopoDS.hxx>
 # include <TopoDS_Face.hxx>
@@ -259,6 +260,13 @@ App::DocumentObjectExecReturn* Helix::execute()
 
         fix.LimitTolerance(result, Precision::Confusion() * size * Tolerance.getValue() ); // significant precision reduction due to helical approximation - needed to allow fusion to succeed
 
+        // try to auto-fix possible invalid result
+        ShapeFix_Solid fixer;
+        fixer.Init(TopoDS::Solid(result));
+        if (fixer.Perform()) {
+            result = fixer.Solid();
+        }
+
         AddSubShape.setValue(result);
 
         if (base.isNull()) {