usbredir: fix buffer-overflow on vmload

usbredir: fix buffer-overflow on vmload

If interface_count is NO_INTERFACE_INFO, let's not access the arrays
out-of-bounds.

==994==ERROR: AddressSanitizer: heap-buffer-overflow on address 0x625000243930 at pc 0x5642068086a8 bp 0x7f0b6f9ffa50 sp 0x7f0b6f9ffa40
READ of size 1 at 0x625000243930 thread T0
    #0 0x5642068086a7 in usbredir_check_bulk_receiving /home/elmarco/src/qemu/hw/usb/redirect.c:1503
    #1 0x56420681301c in usbredir_post_load /home/elmarco/src/qemu/hw/usb/redirect.c:2154
    #2 0x5642068a56c2 in vmstate_load_state /home/elmarco/src/qemu/migration/vmstate.c:168
    #3 0x56420688e2ac in vmstate_load /home/elmarco/src/qemu/migration/savevm.c:829
    #4 0x5642068980cb in qemu_loadvm_section_start_full /home/elmarco/src/qemu/migration/savevm.c:2211
    #5 0x564206899645 in qemu_loadvm_state_main /home/elmarco/src/qemu/migration/savevm.c:2395
    #6 0x5642068998cf in qemu_loadvm_state /home/elmarco/src/qemu/migration/savevm.c:2467
    #7 0x56420685f3e9 in process_incoming_migration_co /home/elmarco/src/qemu/migration/migration.c:449
    #8 0x564207106c47 in coroutine_trampoline /home/elmarco/src/qemu/util/coroutine-ucontext.c:115
    #9 0x7f0c0604e37f  (/lib64/libc.so.6+0x4d37f)

Signed-off-by: Marc-André Lureau <marcandre.lureau@redhat.com>
Reviewed-by: Liam Merwick <liam.merwick@oracle.com>
Reviewed-by: Li Qiang <liq3ea@gmail.com>
Reviewed-by: Philippe Mathieu-Daudé <philmd@redhat.com>
Message-id: 20190807084048.4258-1-marcandre.lureau@redhat.com
Signed-off-by: Gerd Hoffmann <kraxel@redhat.com>