Going back from 'Qif files you have loaded' crashes

Once you have unloaded all files on the above page and go back Gnucash
will crash as it was using an invalid file, check for selected_file in
the ...import_account_prepare function.

gnucash/import-export/qif-imp/assistant-qif-import.c

@@ -2104,21 +2104,32 @@ gnc_ui_qif_import_account_prepare (GtkAssistant  *assistant, gpointer user_data)
 
     if (wind->ask_date_format && wind->date_format)
         qif_import_reparse_dates (wind);
-   /* Determine the next page to display. */
-    if (scm_call_1 (check_from_acct, wind->selected_file) != SCM_BOOL_T)
-    {
-        /* There is an account name missing. Ask the user to provide one. */
-        SCM default_acct = scm_c_eval_string ("qif-file:path-to-accountname");
-        gchar * default_acctname = NULL;
 
-        default_acctname = gnc_scm_call_1_to_string (default_acct, wind->selected_file);
-        gtk_entry_set_text (GTK_ENTRY(wind->acct_entry), default_acctname);
-        g_free (default_acctname);
+    /* make sure there is a file selected, may of come back */
+    if (wind->selected_file == SCM_BOOL_F)
+    {
+        GtkAssistant *assistant = GTK_ASSISTANT(wind->window);
+        gtk_entry_set_text (GTK_ENTRY(wind->filename_entry), "");
+        gtk_assistant_set_current_page (assistant, 1);
     }
     else
     {
-        /* Skip ahead to the "loaded files" page. */
-        gtk_assistant_set_current_page (assistant, num + 1);
+        /* Determine the next page to display. */
+        if (scm_call_1 (check_from_acct, wind->selected_file) != SCM_BOOL_T)
+        {
+            /* There is an account name missing. Ask the user to provide one. */
+            SCM default_acct = scm_c_eval_string ("qif-file:path-to-accountname");
+            gchar * default_acctname = NULL;
+
+            default_acctname = gnc_scm_call_1_to_string (default_acct, wind->selected_file);
+            gtk_entry_set_text (GTK_ENTRY(wind->acct_entry), default_acctname);
+            g_free (default_acctname);
+        }
+        else
+        {
+            /* Skip ahead to the "loaded files" page. */
+            gtk_assistant_set_current_page (assistant, num + 1);
+        }
     }
 }