runtime error: index -1 out of bounds for type 'struct ttx_pop_link[8]'

[kasper93]

SUMMARY: UndefinedBehaviorSanitizer: undefined-behavior ../../src/teletext.c:2646:24 in
../../src/teletext.c:2296:9: runtime error: index -1 out of bounds for type 'struct ttx_pop_link[8]'
    #0 0x7ffa45c450f3 in default_object_invocation F:/dev/zvbi/build/src/../../src/teletext.c:2296:9
    #1 0x7ffa45c31ad5 in vbi_format_vt_page F:/dev/zvbi/build/src/../../src/teletext.c:2762:14
    #2 0x7ffa45c50867 in vbi_fetch_vt_page F:/dev/zvbi/build/src/../../src/teletext.c:2891:13

SUMMARY: UndefinedBehaviorSanitizer: undefined-behavior ../../src/teletext.c:2296:9 in
../../src/teletext.c:2299:10: runtime error: index -1 out of bounds for type 'struct ttx_pop_link[8]'
    #0 0x7ffa45c45394 in default_object_invocation F:/dev/zvbi/build/src/../../src/teletext.c:2299:10
    #1 0x7ffa45c31ad5 in vbi_format_vt_page F:/dev/zvbi/build/src/../../src/teletext.c:2762:14
    #2 0x7ffa45c50867 in vbi_fetch_vt_page F:/dev/zvbi/build/src/../../src/teletext.c:2891:13