App: fix Link extensionGetPropertyByName()

Do not query linked object if the owner object has property with the
given name.

src/App/Link.cpp

@@ -34,6 +34,7 @@
 #include "Link.h"
 #include "LinkBaseExtensionPy.h"
 #include <Base/Console.h>
+#include <Base/Tools.h>
 #include "ComplexGeoData.h"
 #include "ComplexGeoDataPy.h"
 
@@ -1421,14 +1422,21 @@ static bool isExcludedProperties(const char *name) {
 }
 
 Property *LinkBaseExtension::extensionGetPropertyByName(const char* name) const {
-    auto prop = inherited::extensionGetPropertyByName(name);
-    if(prop || isExcludedProperties(name))
-        return prop;
+    if (checkingProperty)
+        return inherited::extensionGetPropertyByName(name);
+    Base::StateLocker guard(checkingProperty);
+    if(isExcludedProperties(name))
+        return nullptr;
     auto owner = getContainer();
-    if(owner && owner->canLinkProperties()) {
-        auto linked = getTrueLinkedObject(true);
-        if(linked)
-            return linked->getPropertyByName(name);
+    if (owner) {
+        App::Property *prop = owner->getPropertyByName(name);
+        if(prop)
+            return prop;
+        if(owner->canLinkProperties()) {
+            auto linked = getTrueLinkedObject(true);
+            if(linked)
+                return linked->getPropertyByName(name);
+        }
     }
     return 0;
 }

src/App/Link.h

@@ -319,6 +319,8 @@ protected:
     mutable bool enableLabelCache;
 
     bool hasOldSubElement;
+
+    mutable bool checkingProperty = false;
 };
 
 ///////////////////////////////////////////////////////////////////////////