OpenGLRenderer: Fix FboFramebuffer making context switches

When a window was created and rendered onto, FBO rendering was made on the device reference context which required a context switch.

This has been fixed with OpenGLFboFramebuffer managing a per-context framebuffer and creating one when needed

include/Nazara/OpenGLRenderer/OpenGLFboFramebuffer.inl

@@ -7,9 +7,9 @@
 
 namespace Nz
 {
-	inline const Vector2ui& OpenGLFboFramebuffer::GetAttachmentSize(std::size_t i) const
+	inline Vector2ui OpenGLFboFramebuffer::GetAttachmentSize(std::size_t i) const
 	{
-		return m_attachmentSizes[i];
+		return Vector2ui(m_attachments[i]->GetSize());
 	}
 }