Fix #3401 warning on multiple solid

- PartDesign only uses the first result shape
  of an operation and discards the rest without
  warning.

- this also fixes #1707

src/Mod/PartDesign/App/FeatureGroove.cpp

@@ -155,6 +155,11 @@ App::DocumentObjectExecReturn *Groove::execute(void)
             TopoDS_Shape solRes = this->getSolid(mkCut.Shape());
             if (solRes.IsNull())
                 return new App::DocumentObjectExecReturn("Resulting shape is not a solid");
+
+            int solidCount = countSolids(result);
+            if (solidCount > 1) {
+                return new App::DocumentObjectExecReturn("Groove: Result has multiple solids. Check parameters.");
+            }
 
             solRes = refineShapeIfActive(solRes);
             this->Shape.setValue(getSolid(solRes));