LibGL: Set GL error on some calls during begin/end

According to the OpenGL 2.x spec, some calls will set the current
global error to `GL_INVALID_OPERATION` if they are used during
a `glBegin`/`glEnd` block.

Userland/Libraries/LibGL/SoftwareGLContext.h

@@ -52,6 +52,7 @@ private:
     Vector<GLTriangle> processed_triangles;
 
     GLenum m_error = GL_NO_ERROR;
+    bool m_in_draw_state = false;
 };
 
 }