pupnp: NULL pointer dereference in ixmlNode_compare crashes on non-namespaced attributes

pupnp is an SDK for development of UPnP device and control point applications. Prior to 2.0.2, ixmlNode_compare in ixml/src/node.c passes the nullable nodeValue, namespaceURI, prefix, and localName fields directly to strcmp. Non-namespaced attributes created by ixmlDocument_createAttribute legitimately leave those fields NULL. When ixmlElement_removeAttributeNode compares two distinct attribute objects with the same nodeName through find_condition_node, the pointer-identity shortcut does not apply and the comparison dereferences NULL, causing a process crash when application handling of attacker-controlled XML reaches this path. This issue is fixed in 2.0.2.