Fix null dereference in moduleNeedsUpdate when the module isn't visible

CHANGELOG.md

@@ -31,6 +31,7 @@ This project adheres to [Semantic Versioning](http://semver.org/).
 - Installation script problems with raspbian
 - Calendar: only show repeating count if the event is actually repeating [#1534](https://github.com/MichMich/MagicMirror/pull/1534)
 - Calendar: Fix exdate handling when multiple values are specified (comma separated)
+- Fix null dereference in moduleNeedsUpdate when the module isn't visible
 
 ### New weather module
 - Fixed weather forecast table display [#1499](https://github.com/MichMich/MagicMirror/issues/1499).

js/main.js

@@ -173,6 +173,10 @@ var MM = (function() {
 	 */
 	var moduleNeedsUpdate = function(module, newHeader, newContent) {
 		var moduleWrapper = document.getElementById(module.identifier);
+		if (moduleWrapper === null) {
+			return false;
+		}
+
 		var contentWrapper = moduleWrapper.getElementsByClassName("module-content");
 		var headerWrapper = moduleWrapper.getElementsByClassName("module-header");