Fix formatting in bbutton.tex

git-svn-id: https://svn.wxwidgets.org/svn/wx/wxWidgets/trunk@36113 c3d73ce0-8a6f-49c7-b76d-6d57e0e08775

docs/latex/wx/bbutton.tex

@@ -31,6 +31,7 @@ the selected state, unpressed focused state, and greyed-out state may be supplie
 This class supports bitmaps for several different states:
 
 \twocolwidtha{5cm}
+\begin{twocollist}\itemsep=0pt
 \twocolitem{\windowstyle{normal}}{This is the bitmap shown in the default state,
 it must be always valid while all the other bitmaps are optional and don't have
 to be set.}