migration/xen: Check return value of qemu_fclose

QEMUFile uses buffered IO so when writing small amounts (such as the Xen
device state file), the actual write call and any errors that may occur
only happen as part of qemu_fclose(). Therefore, report IO errors when
saving the device state under Xen by checking the return value of
qemu_fclose().

Signed-off-by: Ross Lagerwall <ross.lagerwall@citrix.com>
Message-Id: <20180206163039.23661-1-ross.lagerwall@citrix.com>
Signed-off-by: Dr. David Alan Gilbert <dgilbert@redhat.com>
Reviewed-by: Dr. David Alan Gilbert <dgilbert@redhat.com>

migration/savevm.c

@@ -2284,8 +2284,7 @@ void qmp_xen_save_devices_state(const char *filename, bool has_live, bool live,
     f = qemu_fopen_channel_output(QIO_CHANNEL(ioc));
     object_unref(OBJECT(ioc));
     ret = qemu_save_device_state(f);
-    qemu_fclose(f);
-    if (ret < 0) {
+    if (ret < 0 || qemu_fclose(f) < 0) {
         error_setg(errp, QERR_IO_ERROR);
     } else {
         /* libxl calls the QMP command "stop" before calling