Improve QBuffer autotest

The documentation of QIODevice::pos() states: "For sequential devices or
closed devices, where there is no concept of a "current position", 0 is
returned".  The test had a disabled check for a position of -1 before
the device is opened.  Make the test agree with the documentation.

Change-Id: Ide5729bfc825cdb84caf4851574a57d3ef42ccb2
Reviewed-by: Rohan McGovern <rohan.mcgovern@nokia.com>

tests/auto/corelib/io/qbuffer/tst_qbuffer.cpp

@@ -328,9 +328,8 @@ void tst_QBuffer::seekTest()
 
     QByteArray ba;
     QBuffer buf(&ba);
-#if 0
-    QCOMPARE(buf.pos(), qint64(-1));
-#endif
+    QCOMPARE(buf.pos(), qint64(0));
+
     buf.open(QIODevice::ReadWrite);
     QCOMPARE(buf.pos(), qint64(0));