IMAP: fix uidNext implementation

git-svn-id: http://svn.code.sf.net/p/davmail/code/trunk@2187 3d1905a2-6b24-0410-a738-b14d5a86fcbd

src/java/davmail/exchange/ExchangeSession.java

@@ -1629,7 +1629,10 @@ public abstract class ExchangeSession {
                     recent++;
                 }
             }
-            long computedUidNext = messages.get(messages.size() - 1).getImapUid() + 1;
+            long computedUidNext = 1;
+            if (!messages.isEmpty()) {
+                computedUidNext = messages.get(messages.size() - 1).getImapUid() + 1;
+            }
             if (computedUidNext > uidNext) {
                 uidNext = computedUidNext;
             }