failsafe on note update

inc/note.php

@@ -59,7 +59,7 @@ class Note extends PhpObject {
 	public function setNote($sNotes) {
 		$sError = '';
 		
-		if($this->iUserId > 0 && $this->iCourseId > 0) {
+		if($this->iUserId > 0 && $this->iCourseId > 0 && $sNotes!='') {
 			$asData = array_merge($this->getNoteKeys(), array('notes'=>$sNotes));
 			$iNoteId = $this->oDb->insertUpdateRow(self::NOTE_TABLE, $asData, array_keys($this->getNoteKeys()));
 			if(!$iNoteId) $sError = $this->oDb->getLastError();