STYLE: Fix parentheses warning in qMRMLSceneHierarchyModel

This commit fixes a warning introduced by r23845 (BUG: 3926. Added
null pointer checks into reparenting code.)

//----------------
/path/to/Slicer/Libs/MRML/Widgets/qMRMLSceneHierarchyModel.cxx: In member function ‘virtual bool qMRMLSceneHierarchyModel::reparent(vtkMRMLNode, vtkMRMLNode)’:
/path/to/Slicer/Libs/MRML/Widgets/qMRMLSceneHierarchyModel.cxx:306:39: warning: suggest parentheses around ‘&&’ within ‘||’ [-Wparentheses]
if (!hierarchyNode || newParent && strcmp(newParent->GetClassName(), hierarchyNode->GetClassName()))
^
//----------------

git-svn-id: http://svn.slicer.org/Slicer4/trunk@23948 3bd1e089-480b-0410-8dfb-8563597acbee