Description of problem:
nbdkit partition filter can't access  uefi image with option partition-sectorsize=4K 

Version-Release number of selected component (if applicable):
nbdkit-1.36.1-1.el9.x86_64

How reproducible:
100%

Steps to Reproduce:
1.  Access a uefi image with option partition-sectorsize=4K 

   # nbdkit -filter=partition file /var/lib/libvirt/images/Auto-esx8.0-rhell9.3-efi-with-empty-cdrom-sda partition=1 partition-sectorsize=4K  -run 'nbdinfo $uri' 
    nbdkit: file[1]: error: rejecting GPT protective entry from MBR, if the underlying storage uses 4K sectors try using partition-sectorsize=4k
    nbdkit: file[1]: error: rejecting GPT protective entry from MBR, if the underlying storage uses 4K sectors try using partition-sectorsize=4k
    nbdkit: file[1]: error: rejecting GPT protective entry from MBR, if the underlying storage uses 4K sectors try using partition-sectorsize=4k
    nbdinfo: nbd_opt_go: server replied with error to opt_go request: No such file or directory for the default export
    nbdinfo: suggestion: to list all exports on the server, use --list
    protocol: newstyle-fixed without TLS, using structured packets

2.  Access a non-uefi image with option partition-sectorsize=4K 

1.  nbdkit -filter=partition file /var/lib/libvirt/images/esx8.0-rhel8.6-x86_64-sda partition=1 partition-sectorsize=4K  -run 'nbdinfo $uri' 
   protocol: newstyle-fixed without TLS, using structured packets
   export="":
       export-size: 8589934592 (8G)
       content: data
       uri: nbd+unix:///?socket=/tmp/nbdkito6uRTa/socket
       contexts:
           base:allocation
       is_rotational: false
       is_read_only: false
       can_block_status_payload: false
       can_cache: true
       can_df: true
       can_fast_zero: false
       can_flush: true
       can_fua: true
       can_multi_conn: true
       can_trim: true
       can_zero: true

   
Actual results:
As above description

Expected result:
nbdkit partition filter can access  uefi image with option partition-sectorsize=4K 

Additional info:
1. Access a uefi image without option partition-sectorsize

   # nbdkit --filter=partition file /var/lib/libvirt/images/Auto-esx8.0-rhell9.3-efi-with-empty-cdrom-sda partition=1   --run 'nbdinfo $uri' 
    protocol: newstyle-fixed without TLS, using structured packets
    export="":
        export-size: 629145600 (600M)
        content: DOS/MBR boot sector, code offset 0x58+2, OEM-ID "mkfs.fat", sectors/cluster 8, Media descriptor 0xf8, sectors/track 32, heads 64, hidden sectors 2048, sectors 1228800 (volumes > 32 MB), FAT (32 bit), sectors/FAT 1200, reserved 0x1, serial number 0xb10ec180, unlabeled
        uri: nbd+unix:///?socket=/tmp/nbdkitWD9of8/socket
        contexts:
            base:allocation
        is_rotational: false
        is_read_only: false
        can_block_status_payload: false
        can_cache: true
        can_df: true
        can_fast_zero: false
        can_flush: true
        can_fua: true
        can_multi_conn: true
        can_trim: true
        can_zero: true

2. Access a uefi image with option partition-sectorsize=512

   # nbdkit --filter=partition file /var/lib/libvirt/images/Auto-esx8.0-rhell9.3-efi-with-empty-cdrom-sda partition=1 partition-sectorsize=512 --run 'nbdinfo $uri' 
    protocol: newstyle-fixed without TLS, using structured packets
    export="":
        export-size: 629145600 (600M)
        content: DOS/MBR boot sector, code offset 0x58+2, OEM-ID "mkfs.fat", sectors/cluster 8, Media descriptor 0xf8, sectors/track 32, heads 64, hidden sectors 2048, sectors 1228800 (volumes > 32 MB), FAT (32 bit), sectors/FAT 1200, reserved 0x1, serial number 0xb10ec180, unlabeled
        uri: nbd+unix:///?socket=/tmp/nbdkitDKAAi8/socket
        contexts:
            base:allocation
        is_rotational: false
        is_read_only: false
        can_block_status_payload: false
        can_cache: true
        can_df: true
        can_fast_zero: false
        can_flush: true
        can_fua: true
        can_multi_conn: true
        can_trim: true
        can_zero: true