Fix implicit cast warning

[codecat]

Fixes this warning:

imgui.h(132): warning C4244: 'argument': conversion from 'const float' to 'int', possible loss of data imgui-sfml.cpp(338): note: see reference to function template instantiation 'ImVec2::operator sf::Vector2<int>(void) const<int>' being compiled 

[eXpl0it3r]

Please use C++' static_cast<>.

Alternative method for converting would be to construct an sf::Vector2f abd pass that to the constructor, then SFML will do the cast.

[codecat]

The mousePos vector is an ImVec2, does imgui-sfml provide an automatic cast for that?

[eliasdaler]

Looks good, thanks!

I should probably re-check all ImVec2 <-> sf::Vector2 conversions and not rely on implicit casts at all in ImGui-SFML's code...