Fix the main crash cause and also forbid empty USB devices as qemu
doesn't accept them.

Peter Krempa (2):
  qemu: block: Allow NULL 'data' in 'qemuBlockStorageSourceChainDetach'
  qemu: validate: Reject empty USB disks

 src/qemu/qemu_block.c                         |  3 ++
 src/qemu/qemu_validate.c                      |  6 ++++
 .../disk-cdrom-bus-other.x86_64-latest.args   |  5 ++--
 .../disk-cdrom-bus-other.x86_64-latest.xml    |  5 ----
 .../qemuxmlconfdata/disk-cdrom-bus-other.xml  |  5 ----
 .../disk-cdrom-usb-empty.x86_64-latest.err    |  1 +
 .../qemuxmlconfdata/disk-cdrom-usb-empty.xml  | 29 +++++++++++++++++++
 tests/qemuxmlconftest.c                       |  1 +
 8 files changed, 42 insertions(+), 13 deletions(-)
 create mode 100644 tests/qemuxmlconfdata/disk-cdrom-usb-empty.x86_64-latest.err
 create mode 100644 tests/qemuxmlconfdata/disk-cdrom-usb-empty.xml

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2.46.0