Dav: Avoid returning null in getCmdBasePath

git-svn-id: http://svn.code.sf.net/p/davmail/code/trunk@1756 3d1905a2-6b24-0410-a738-b14d5a86fcbd

src/java/davmail/exchange/dav/DavExchangeSession.java

@@ -227,7 +227,7 @@ public class DavExchangeSession extends ExchangeSession {
      * @return cmd base path
      */
     public String getCmdBasePath() {
-        if (PUBLIC_ROOT.equals(publicFolderUrl)) {
+        if (PUBLIC_ROOT.equals(publicFolderUrl) && mailPath != null) {
             // public folder is not available => try to use mailbox path
             // Note: This does not work with freebusy, which requires /public/
             return mailPath;