Restructure monitor enumeration

This way is both kinder on event-based enumeration and less work to
unwind allocations for when properly implementing GLFW_OUT_OF_MEMORY.

src/x11_init.c

@@ -794,6 +794,7 @@ int _glfwPlatformInit(void)
 
     _glfwInitTimerPOSIX();
 
+    _glfwPollMonitorsX11();
     return GLFW_TRUE;
 }