Correct Issue 19980 for the 1.0 tree

Make no Change notification if an object's Label, after making it Unique and letting OnBeforeChangeLabel alter it, ends up equal to its current value.

src/App/PropertyStandard.cpp

@@ -1389,6 +1389,10 @@ void PropertyString::setValue(const char* newLabel)
         obj->onBeforeChangeLabel(label);
         newLabel = label.c_str();
 
+        if (newLabel == _cValue) {
+            return;
+        }
+
         if(!obj->getDocument()->testStatus(App::Document::Restoring)) {
             // Only update label reference if we are not restoring. When
             // importing (which also counts as restoring), it is possible the