fix: Cannot read property 'slick' of undefined issue when navigating

Author: Mark

Diff for: package.json

@@ -1,6 +1,6 @@
 {
   "name": "ngx-slick",
-  "version": "0.2.0",
+  "version": "0.2.1",
   "scripts": {
     "build": "gulp build",
     "build:watch": "gulp",

Diff for: src/package.json

@@ -1,6 +1,6 @@
 {
   "name": "ngx-slick",
-  "version": "0.2.0",
+  "version": "0.2.1",
   "repository": {
     "type": "git",
     "url": "https://github.com/devmark/ngx-slick"

Diff for: src/slick.component.ts

@@ -153,9 +153,12 @@ export class SlickComponent implements AfterViewInit, OnDestroy {
     }
 
     public unslick() {
-        this.zone.run(() => {
-            this.$instance.slick('unslick');
-        });
+        if (this.$instance) {
+            this.zone.run(() => {
+                this.$instance.slick('unslick');
+            });
+        }
+        this.initialized = false;
     }
 
 }