Add SDL_Window to initGraphicsContext prototype

This value is needed for vulkan to properly allocate a surface, and would benefit OpenGL to move more of its initialization code into here rather than in `emulator.cpp`.

include/renderer_null/renderer_null.hpp

@@ -9,7 +9,7 @@ class RendererNull final : public Renderer {
 
 	void reset() override;
 	void display() override;
-	void initGraphicsContext() override;
+	void initGraphicsContext(SDL_Window* window) override;
 	void clearBuffer(u32 startAddress, u32 endAddress, u32 value, u32 control) override;
 	void displayTransfer(u32 inputAddr, u32 outputAddr, u32 inputSize, u32 outputSize, u32 flags) override;
 	void drawVertices(PICA::PrimType primType, std::span<const PICA::Vertex> vertices) override;