QRingBuffer: simplify QRingChunk::detach()

Just use the QByteArray(ptr, n) ctor instead of the (n,
Qt::Uninitialized) one + memcpy() + std::move().

Pick-to: 6.3
Change-Id: I127219c21556e683d15136f7e6f7b3576b7b2444
Reviewed-by: Mårten Nordheim <marten.nordheim@qt.io>

src/corelib/tools/qringbuffer.cpp

@@ -57,9 +57,7 @@ void QRingChunk::detach()
     Q_ASSERT(isShared());
 
     const qsizetype chunkSize = size();
-    QByteArray x(chunkSize, Qt::Uninitialized);
-    ::memcpy(x.data(), chunk.constData() + headOffset, chunkSize);
-    chunk = std::move(x);
+    chunk = QByteArray(std::as_const(*this).data(), chunkSize);
     headOffset = 0;
     tailOffset = chunkSize;
 }