QCryptographicHash: make narrowing in addData(QIODevice*) explicit

QIODevice::read(ptr, n) returns qint64, not int. The returned values
are, however, confined to the interval [-1,1024], so no harm
done. Make the narrowing explicit, though.

Pick-to: 6.5
Change-Id: I5f95292ca6e05f0f402e7258e590593eff361255
Reviewed-by: Mårten Nordheim <marten.nordheim@qt.io>
Reviewed-by: Thiago Macieira <thiago.macieira@intel.com>

src/corelib/tools/qcryptographichash.cpp

@@ -696,10 +696,10 @@ bool QCryptographicHash::addData(QIODevice *device)
         return false;
 
     char buffer[1024];
-    int length;
+    qint64 length;
 
     while ((length = device->read(buffer, sizeof(buffer))) > 0)
-        d->addData({buffer, length});
+        d->addData({buffer, qsizetype(length)}); // length always <= 1024
 
     return device->atEnd();
 }