TestSocketLineReader: Ensure we provide a more appropiate message if we fail trying to open a connection to the client

A litle irrelevant change :)

BTW, I'm encounter this test error on Debian kfreebsd i386:
  https://buildd.debian.org/status/fetch.php?pkg=kdeconnect&arch=kfreebsd-i386&ver=0.7-1&stamp=1404242653

Maybe someone have a clue on what is happening here :)

REVIEW: 119091

tests/testsocketlinereader.cpp

@@ -79,6 +79,9 @@ void TestSocketLineReader::socketLineReader()
     }
 
     QTcpSocket *sock = mServer->nextPendingConnection();
+
+    QVERIFY2(sock != 0, "Could not open a connection to the client");
+
     mReader = new SocketLineReader(sock, this);
     connect(mReader, SIGNAL(readyRead()), SLOT(newPackage()));
     mTimer.start();