Exercise: Fix condition when update questions

public/main/exercise/answer.class.php

@@ -785,19 +785,16 @@ class Answer
 
         if (count($this->position) > $this->new_nbrAnswers) {
             $i = $this->new_nbrAnswers + 1;
-            if (isset($this->position[$i])) {
+            while (isset($this->position[$i])) {
-                while ($this->position[$i]) {
                 $position = $this->position[$i];
                 $sql = "DELETE FROM $answerTable
                     WHERE
-                            c_id = {$this->course_id} AND
                         question_id = '".$questionId."' AND
                         position ='$position'";
                 Database::query($sql);
                 $i++;
             }
         }
-        }
 
         // moves $new_* arrays
         $this->answer = $this->new_answer;