Gui: modernize C++: use range-based for loop

src/Gui/Selection.cpp

@@ -1150,8 +1150,7 @@ bool SelectionSingleton::addSelection(const SelectionObject& obj, bool clearPres
     }
     else if (!subNames.empty()) {
         bool ok = true;
-        for (std::size_t i=0; i<subNames.size(); i++) {
-            const std::string& name = subNames[i];
+        for (const std::string& name : subNames) {
             ok &= addSelection(obj.getDocName(), obj.getFeatName(), name.c_str());
         }
         return ok;