QHttpNetworkHeaderPrivate: use QList<QByteArray>::join()

...instead of coding the loop by hand.

Change-Id: Ieaa066de1ff8552b737cf27cf0d4236efb7296eb
Reviewed-by: Olivier Goffart (Woboq GmbH) <ogoffart@woboq.com>

src/network/access/qhttpnetworkheader.cpp

@@ -79,16 +79,8 @@ QByteArray QHttpNetworkHeaderPrivate::headerField(const QByteArray &name, const
     QList<QByteArray> allValues = headerFieldValues(name);
     if (allValues.isEmpty())
         return defaultValue;
-
-    QByteArray result;
-    bool first = true;
-    foreach (const QByteArray &value, allValues) {
-        if (!first)
-            result += ", ";
-        first = false;
-        result += value;
-    }
-    return result;
+    else
+        return allValues.join(", ");
 }
 
 QList<QByteArray> QHttpNetworkHeaderPrivate::headerFieldValues(const QByteArray &name) const