Tidy up answer-test generated notes in matrix, and more robust check they are non-empty.

Author: sangwinc

stack/maxima/stackmaxima.mac

@@ -1652,7 +1652,7 @@ ATMatrix(SA, SB) := block([RawMark, FeedBack, AnswerNote, str, ret, SAr, SAc, SB
         retnew:ATAlgEquivfun(SA[kloop], SB[kloop]),
         ret[1]:ret[1] and retnew[1],
         ret[2]:ret[2] and retnew[2],
-        ret[3]:concat(ret[3], " ", retnew[3]),
+        ret[3]:strim(" ", concat(ret[3], " ", retnew[3])),
         if retnew[2] = false then AddFeedBack:true
     ),
     if AddFeedBack = true then block(

stack/prt.evaluatable.class.php

@@ -272,8 +272,14 @@ public function get_answernotes($atnotes = true) {
         }
         $i = 0;
         foreach ($path as $atresult) {
-            if ($atnotes && ($atresult[2] !== '""')) {
-                $notes[] = trim($atresult[2]);
+            if ($atnotes) {
+                // Some answer test notes are non-empty whitespace string, e.g. "    ";
+                $note = trim($atresult[2]);
+                // Strip off "" and trim.
+                $note = trim(substr($note, 1, strlen($note) - 2));
+                if ($note !== '') {
+                    $notes[] = trim($atresult[2]);
+                }
             }
             // We need to check the array_key_exists because in the case of a guard clause it will not.
             // Do we actually want to ignore the missing note here or indicate the note is missing with a note?