Fixes StringIndexOutOfBoundsException when tab is pressed in the write

panel in the chat room window to search for contact and the pattern is
empty string. Patch provided by Danny van Heumen.

src/net/java/sip/communicator/impl/gui/main/chat/ChatWritePanel.java

@@ -615,6 +615,13 @@ else if(e.getKeyCode() == KeyEvent.VK_TAB)
 
             String sequence = message.substring(position, index);
             
+            if (sequence.length() <= 0)
+            {
+                // Do not look for matching contacts if the matching pattern is
+                // 0 chars long, since all contacts will match.
+                return;
+            }
+            
             Iterator<ChatContact<?>> iter = chatPanel.getChatSession()
                                              .getParticipants();
             ArrayList<String> contacts = new ArrayList<String>();