Viewer: Truncate overly long conn. history strings

Java Preferences values cannot be more than Preferences.MAX_VALUE_LENGTH
(usually 8192) characters in length.  Attempting to store a longer
string into a Preferences node results in an IllegalArgumentException.

Fixes #410

java/com/turbovnc/vncviewer/ServerDialog.java

@@ -1,4 +1,5 @@
-/* Copyright (C) 2012-2015, 2018, 2020 D. R. Commander. All Rights Reserved.
+/* Copyright (C) 2012-2015, 2018, 2020, 2024 D. R. Commander.
+ * All Rights Reserved.
  * Copyright (C) 2011-2013 Brian P. Hinz
  * Copyright (C) 2002-2005 RealVNC Ltd. All Rights Reserved.
  *
@@ -26,6 +27,7 @@
 import javax.swing.border.*;
 import javax.swing.WindowConstants.*;
 import java.util.*;
+import java.util.prefs.Preferences;
 
 import com.turbovnc.rdr.*;
 import com.turbovnc.rfb.*;
@@ -246,7 +248,16 @@ private boolean commit() {
  sb.append(str);
  }
  }
- UserPreferences.set("ServerDialog", "history", sb.toString());
+ String history = sb.toString();
+ if (history.length() > Preferences.MAX_VALUE_LENGTH) {
+ int lastComma =
+ history.lastIndexOf(',', Preferences.MAX_VALUE_LENGTH);
+ if (lastComma <= 0)
+ history = "";
+ else
+ history = history.substring(0, lastComma);
+ }
+ UserPreferences.set("ServerDialog", "history", history);
  UserPreferences.save("ServerDialog");
 
  } catch (Exception e) {