fix fetching duplication

app/src/main/java/awais/instagrabber/customviews/helpers/PostFetcher.java

@@ -17,12 +17,14 @@ public class PostFetcher {
     }
 
     public void fetch() {
+        if (!fetching) {
             fetching = true;
             postFetchService.fetch(result -> {
                 fetching = false;
                 fetchListener.onResult(result);
             });
         }
+    }
 
     public void reset() {
         postFetchService.reset();