`copy` is documented as possibly returning a smaller number of bytes
than requested. In practice, this can occur if a block is cached and the
reader never pulls in the file to check its size.
Bug: 565874
Change-Id: I1e53b3d2f4ab09334178934dc0ef74ea99045cd3
Signed-off-by: wh <wh9692@protonmail.com>
Signed-off-by: Matthias Sohn <matthias.sohn@sap.com>