Part/Toponaming: Transfer WireJoiner

* Added test for WireJoiner::getResultWires()
 * Replaced references in test for WireJoiner::getOpenWires() with more correct references
 * Added a comment in WireJoiner::WireJoinerP::getResultWires() to better explain how it works

Signed-off-by: CalligaroV <vincenzo.calligaro@gmail.com>

src/Mod/Part/App/WireJoiner.cpp

@@ -2297,6 +2297,10 @@ public:
     }
 
     bool getResultWires(TopoShape &shape, const char *op) {
+        // As compound is created by various calls to builder.MakeCompound() it looks that the
+        // following condition is always false.
+        // Probably it may be needed to add something like compound.Nullify() as done for
+        // openWireCompound in WireJoiner::WireJoinerP::clear()
         if (compound.IsNull()) {
             shape.setShape(TopoShape());
             return false;