prevent crashes after detach in manage security token fragment

OpenKeychain/src/main/java/org/sufficientlysecure/keychain/ui/token/ManageSecurityTokenContract.java

@@ -30,6 +30,7 @@ import org.sufficientlysecure.keychain.ui.token.ManageSecurityTokenFragment.Stat
 class ManageSecurityTokenContract {
     interface ManageSecurityTokenMvpPresenter {
         void setView(ManageSecurityTokenMvpView createSecurityTokenImportFragment);
+        void detach();
         void onActivityCreated();
 
         void onClickRetry();

OpenKeychain/src/main/java/org/sufficientlysecure/keychain/ui/token/ManageSecurityTokenFragment.java

@@ -145,7 +145,7 @@ public class ManageSecurityTokenFragment extends Fragment implements ManageSecur
     public void onDestroyView() {
         super.onDestroyView();
 
-        presenter.setView(null);
+        presenter.detach();
     }
 
     @Override

OpenKeychain/src/main/java/org/sufficientlysecure/keychain/ui/token/ManageSecurityTokenPresenter.java

@@ -81,6 +81,16 @@ class ManageSecurityTokenPresenter implements ManageSecurityTokenMvpPresenter {
         this.view = view;
     }
 
+    @Override
+    public void detach() {
+        this.view = null;
+
+        loaderManager.destroyLoader(LOADER_LOCAL);
+        loaderManager.destroyLoader(LOADER_URI);
+        loaderManager.destroyLoader(LOADER_KEYSERVER);
+        loaderManager.destroyLoader(LOADER_CONTENT_URI);
+    }
+
     @Override
     public void onActivityCreated() {
         if (!checkedKeyStatus || !searchedLocally || !searchedAtUri || !searchedKeyservers) {
@@ -143,6 +153,10 @@ class ManageSecurityTokenPresenter implements ManageSecurityTokenMvpPresenter {
         new Handler().postDelayed(new Runnable() {
             @Override
             public void run() {
+                if (view == null) {
+                    return;
+                }
+
                 performKeyCheck();
             }
         }, 1000);
@@ -220,10 +234,6 @@ class ManageSecurityTokenPresenter implements ManageSecurityTokenMvpPresenter {
 
         @Override
         public void onLoadFinished(Loader<KeyRetrievalResult> loader, KeyRetrievalResult data) {
-            if (view == null) {
-                return;
-            }
-
             switch (loader.getId()) {
                 case LOADER_LOCAL: {
                     searchedLocally = true;