Make NETRootInfo initialization reasonable

The documentation of NETRootInfo::activate() says that it should be
called after creating the NETRootInfo object to read properties.

However, it's called in two places: VirtualDesktopManager::setRows()
and Workspace::initializeX11(). At quick glance, there's no justifying
reason to call activate() in setRows(), it doesn't fit the purpose
of setRows().

This change re-arranges NETRootInfo initialization code so it makes
more sense.

src/virtualdesktops.cpp

@@ -610,7 +610,6 @@ void VirtualDesktopManager::setRows(uint rows)
     }
     if (m_rootInfo) {
         m_rootInfo->setDesktopLayout(NET::OrientationHorizontal, columns, m_rows, NET::DesktopLayoutCornerTopLeft);
-        m_rootInfo->activate();
     }
 
     updateLayout();

src/workspace.cpp

@@ -303,9 +303,10 @@ void Workspace::initializeX11()
     m_nullFocus->map();
 
     RootInfo *rootInfo = RootInfo::create();
+    rootInfo->activate();
+
     const auto vds = VirtualDesktopManager::self();
     vds->setRootInfo(rootInfo);
-    rootInfo->activate();
 
     // TODO: only in X11 mode
     // Extra NETRootInfo instance in Client mode is needed to get the values of the properties