[Libreoffice] Build failure in writer/sw/source/ui/index/cnttab.cxx

The last commit in writer has introduced a bug which prevents a build
from completing:

[...]
/home/ftigeot/Projects/LibreOffice/bootstrap/clone/writer/sw/source/ui/index/cnttab.cxx: In member 
function 'void SwTokenWindow::RemoveControl(SwTOXButton*, sal_Bool)':
/home/ftigeot/Projects/LibreOffice/bootstrap/clone/writer/sw/source/ui/index/cnttab.cxx:3212: 
error: no match for 'operator!=' in 'it != std::vector<_Tp, _Alloc>::rbegin() [with _Tp = Control*, 
_Alloc = std::allocator<Control*>]()'
/home/ftigeot/Projects/LibreOffice/bootstrap/solver/330/unxdflyx3.pro/inc/tools/fract.hxx:139: 
note: candidates are: bool operator!=(const Fraction&, const Fraction&)
dmake:  Error code 1, while making '../../../unxdflyx3.pro/slo/cnttab.obj'


Code around line 3212 of cnttab.cxx looks like:

    // the two neighbours of the box must be merged
    // the properties of the right one will be lost
    OSL_ENSURE(it != aControlList.begin() && it != aControlList.rbegin(),
        "Button at first or last position?");

I believe there should be a cast to const somewhere for aControlList.rbegin()
but I am no C++ programmer and cannot write a fix for this expression.

-- 
Francois Tigeot