Given that the block size is read from the header of the VDI file, a
wide variety of sizes might be seen. Rather than re-using a block
sized memory region when writing the VDI header, allocate an
appropriately sized buffer.

Signed-off-by: David Edmondson <david.edmondson@oracle.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
Acked-by: Max Reitz <mreitz@redhat.com>
Message-id: 20210325112941.365238-3-pbonzini@redhat.com
Message-Id: <20210309144015.557477-3-david.edmondson@oracle.com>
Acked-by: Max Reitz <mreitz@redhat.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
Signed-off-by: Stefan Hajnoczi <stefanha@redhat.com>