trunk doesn't compile with new XHTML code

[Uwe Stöhr]

I get

InsetBox.cpp
d:\lyxsvn\lyx-devel\src\insets\insetbox.cpp(494) : error C4716: 'lyx::InsetBox::xhtml' : must return 
a value
scons: *** [release\src\insets\InsetBox.obj] Error 2
scons: building terminated because of errors.
regards Uwe