db/upnp/Directory: merge m_containers and m_items

There is no use in duplicating these containers.  It only means that
we have to search both, duplicating the code.

src/db/upnp/Directory.cxx

@@ -149,15 +149,9 @@ protected:
 
 	virtual void EndElement(const XML_Char *name)
 	{
-		if (!strcmp(name, "container")) {
-			if (checkobjok()) {
-				m_dir.m_containers.push_back(m_tobj);
-			}
-		} else if (!strcmp(name, "item")) {
-			if (checkobjok()) {
-				m_dir.m_items.push_back(m_tobj);
-			}
-		}
+		if ((!strcmp(name, "container") || !strcmp(name, "item")) &&
+		    checkobjok())
+			m_dir.objects.push_back(m_tobj);
 
 		m_path.pop_back();
 	}

src/db/upnp/Directory.hxx

@@ -21,6 +21,7 @@
 #define MPD_UPNP_DIRECTORY_HXX
 
 #include "Object.hxx"
+#include "Compiler.h"
 
 #include <string>
 #include <vector>
@@ -33,8 +34,16 @@ class Error;
  */
 class UPnPDirContent {
 public:
-	std::vector<UPnPDirObject> m_containers;
-	std::vector<UPnPDirObject> m_items;
+	std::vector<UPnPDirObject> objects;
+
+	gcc_pure
+	const UPnPDirObject *FindObject(const char *name) const {
+		for (const auto &o : objects)
+			if (o.name == name)
+				return &o;
+
+		return nullptr;
+	}
 
 	/**
 	 * Parse from DIDL-Lite XML data.