Fix regression in itemId detection

git-svn-id: http://svn.code.sf.net/p/davmail/code/trunk@2205 3d1905a2-6b24-0410-a738-b14d5a86fcbd

src/java/davmail/exchange/ews/EwsExchangeSession.java

@@ -2450,8 +2450,8 @@ public class EwsExchangeSession extends ExchangeSession {
      */
     protected static boolean isItemId(String itemName) {
         return itemName.length() >= 152
-                // item name is base64
-                && itemName.matches("^([A-Za-z0-9+/]{4})*([A-Za-z0-9+/]{4}|[A-Za-z0-9+/]{3}=|[A-Za-z0-9+/]{2}==)$");
+                // item name is base64url
+                && itemName.matches("^([A-Za-z0-9-_]{4})*([A-Za-z0-9-_]{4}|[A-Za-z0-9-_]{3}=|[A-Za-z0-9-_]{2}==)$");
     }