assert failed when using text search while page still loading

(gdb) bt
#0  0xb778a424 in __kernel_vsyscall ()
#1  0xb70b2661 in *__GI_raise (sig=6)
    at ../nptl/sysdeps/unix/sysv/linux/raise.c:64
#2  0xb70b5a92 in *__GI_abort () at abort.c:92
#3  0xb70ab878 in *__GI___assert_fail (
    assertion=0x816049e "i >= 0 && this->num - i > 0", 
    file=0x816048e "../lout/misc.hh", line=167, 
    function=0x8160540 "T* lout::misc::SimpleVector<T>::getRef(int) const [with T = dw::Textblock::Line]") at assert.c:81
#4  0x080a73f6 in lout::misc::SimpleVector<dw::Textblock::Line>::getRef (
    this=0x905df50, i=-1) at ../lout/misc.hh:167
#5  0x080a8447 in dw::Textblock::TextblockIterator::getAllocation (
    this=0x885ef98, start=0, end=5, allocation=0xbff2e818)
    at textblock_iterator.cc:288
#6  0x080c65f7 in dw::core::Iterator::scrollTo (it1=0x885ef98, it2=0x948efe0, 
    start=0, end=5, hpos=dw::core::HPOS_INTO_VIEW, vpos=dw::core::VPOS_CENTER)
    at iterator.cc:108
#7  0x080c621e in dw::core::DeepIterator::scrollTo (it1=0x88e86e8, 
    it2=0x885efb8, start=0, end=5, hpos=dw::core::HPOS_INTO_VIEW, 
    vpos=dw::core::VPOS_CENTER) at iterator.hh:229
#8  0x080c629a in dw::core::CharIterator::scrollTo (it1=0x89c6e60, 
    it2=0x8872900, hpos=dw::core::HPOS_INTO_VIEW, vpos=dw::core::VPOS_CENTER)
    at iterator.hh:265
#9  0x080c5bcb in dw::core::FindtextState::search (this=0x8a02a40, 
    key=0x88dbd70 "dillo", caseSens=false, backwards=false) at findtext.cc:120
#10 0x08057cad in dw::core::Layout::search (this=0x8a02970, 
    str=0x88dbd70 "dillo", caseSens=false, backwards=0) at ../dw/layout.hh:444
#11 0x080579e5 in a_UIcmd_findtext_search (bw=0x8ae1940, 
    key=0x88dbd70 "dillo", case_sens=0, backward=0) at uicmd.cc:1484
#12 0x0808c7c3 in Findbar::search_cb (vfb=0x8a08808) at findbar.cc:86
#13 0x081075e1 in Fl_Widget::do_callback (this=0x8882020, o=0x8882020, 
    arg=0x8a08808) at Fl_Widget.cxx:328
#14 0x080e305d in do_callback (this=0x8882020) at ../FL/Fl_Widget.H:840
#15 Fl_Button::handle (this=0x8882020, event=12) at Fl_Button.cxx:164
#16 0x080503c9 in TipWinButton::handle (this=0x8882020, e=12) at tipwin.cc:158
#17 0x08050536 in CustButton::handle (this=0x8882020, e=12) at tipwin.cc:194
#18 0x080e4b64 in send (o=o@entry=0x8882020, event=event@entry=12)
    at Fl_Group.cxx:98
#19 0x080e5755 in Fl_Group::handle (this=0x8a08808, event=12)
    at Fl_Group.cxx:185
#20 0x0808cd72 in Findbar::handle (this=0x8a08808, event=12) at findbar.cc:192
#21 0x080e4b64 in send (o=o@entry=0x8a08808, event=event@entry=12)
    at Fl_Group.cxx:98
#22 0x080e5755 in Fl_Group::handle (this=0x88e9218, event=12)
    at Fl_Group.cxx:185
#23 0x08052f2f in UI::handle (this=0x88e9218, event=12) at ui.cc:788
#24 0x080dc5d2 in send (event=event@entry=12, to=to@entry=0x88e9218, 
    window=<optimized out>) at Fl.cxx:1143
#25 0x080dd421 in Fl::handle_ (e=12, window=0x8806268) at Fl.cxx:1401
#26 0x080dd368 in Fl::handle_ (e=8, window=0x8806268) at Fl.cxx:1379
#27 0x0810bbc0 in fl_handle (thisevent=...) at Fl_x.cxx:2144
#28 0x0810d89e in do_queued_events () at Fl_x.cxx:210
#29 0x0810d93f in fl_wait (time_to_wait=0) at Fl_x.cxx:235
#30 0x080de3d2 in Fl::wait (time_to_wait=<optimized out>, 
    time_to_wait@entry=<error reading variable: Could not find type for DW_OP_GNU_const_type>) at Fl.cxx:566
#31 0x080de46e in Fl::run () at Fl.cxx:589
#32 0x0804f933 in main (argc=1, argv=0xbff2f214) at dillo.cc:586

I see that it's unhappy in
Textblock::TextblockIterator::getAllocation() where index was 34 and
lineIndex = textblock->findLineOfWord (index); results in -1, which
the getRef() doesn't want at all...