Added GLFW_VISIBLE to glfwWindowParam.

src/window.c

@@ -723,6 +723,8 @@ GLFWAPI int glfwGetWindowParam(GLFWwindow handle, int param)
             return window->refreshRate;
         case GLFW_RESIZABLE:
             return window->resizable;
+        case GLFW_VISIBLE:
+            return window->visible;
         case GLFW_OPENGL_VERSION_MAJOR:
             return window->glMajor;
         case GLFW_OPENGL_VERSION_MINOR: