QRingBuffer::read(): remove unneeded byte array allocation

QRingBuffer already works fine with empty list of arrays.

Change-Id: I5cd388709686d2980efa3d5129c726e75c0b5c09
Reviewed-by: Oswald Buddenhagen <oswald.buddenhagen@theqtcompany.com>

src/corelib/tools/qringbuffer.cpp

@@ -276,7 +276,6 @@ QByteArray QRingBuffer::read()
     if (tailBuffer == 0) {
         qba.resize(tail);
         tail = 0;
-        buffers.append(QByteArray());
     } else {
         --tailBuffer;
     }