Fix vs2010 build
This fixes a compiler error with VS 2010. The pair template gets this error:
C:\Program Files (x86)\Microsoft Visual Studio 10.0\VC\INCLUDE\utility(163) : error C2440: 'initializing' : cannot convert from 'int' to 'vtkTextProperty *'
Conversion from integral type to pointer type requires reinterpret_cast, C-style cast or function-style cast
C:\Program Files (x86)\Microsoft Visual Studio 10.0\VC\INCLUDE\utility(247) : see reference to function template instantiation 'std::_Pair_base<_Ty1,_Ty2>::_Pair_base<double&,_Ty>(_Other1,_Other2 &&)' being compiled
with
[
_Ty1=double,
_Ty2=vtkTextProperty *,
_Ty=int,
_Other1=double &,
_Other2=int
]
This cast fixes the issue.