gl_rasterizer: Fixup undefined behaviour in SetupDraw

src/video_core/renderer_opengl/gl_rasterizer.cpp

@@ -252,6 +252,7 @@ DrawParameters RasterizerOpenGL::SetupDraw() {
         params.count = regs.vertex_buffer.count;
         params.vertex_first = regs.vertex_buffer.first;
     }
+    return params;
 }
 
 void RasterizerOpenGL::SetupShaders() {