AbstractMyJDClient:
-fixes #50468
-added simple input validation

git-svn-id: svn://svn.jdownloader.org/jdownloader/MyJDownloaderClient@26815 ebf7c1c2-ba36-0410-9fe8-c592906822b4
Started Working on Downloadlist change event system

git-svn-id: svn://svn.jdownloader.org/jdownloader/MyJDownloaderClient@26818 ebf7c1c2-ba36-0410-9fe8-c592906822b4