Merge pull request #2978 from k9mail/GH-2931_do_not_crash_when_closing_ImapConnection_twice

Do nothing in ImapConnection.close() if connection is not open

k9mail-library/src/main/java/com/fsck/k9/mail/store/imap/ImapConnection.java

@@ -715,6 +715,10 @@ class ImapConnection {
     }
 
     public void close() {
+        if (!open) {
+            return;
+        }
+
         open = false;
         stacktraceForClose = new Exception();