Fix bug of search history randomly not saved

Don't create disposable from operation of storing search to history
because as we certainly want this to complete.

Disposable was created in `search` method and then alsmost immediately
was called `startLoading` which disposed "all" disposables including
our operation of search storing (if was unlucky enough to not finish
before this moment)

Author: Yevhen Babiichuk (DustDFG)

app/src/main/java/org/schabi/newpipe/fragments/list/search/SearchFragment.java

@@ -865,14 +865,15 @@ private void search(@NonNull final String theSearchString,
         hideKeyboardSearch();
 
         // store search query if search history is enabled
-        disposables.add(historyRecordManager.onSearched(serviceId, theSearchString)
+
+        historyRecordManager.onSearched(serviceId, theSearchString)
                 .observeOn(AndroidSchedulers.mainThread())
                 .subscribe(
                         ignored -> {
                         },
                         throwable -> showSnackBarError(new ErrorInfo(throwable, UserAction.SEARCHED,
                                 theSearchString, serviceId))
-                ));
+                );
 
         // load search results
         suggestionPublisher.onNext(theSearchString);