API fetch: log the curl errors

classes/session.php

@@ -230,8 +230,7 @@ class mod_labnbook_session
         $response = curl_exec($curl);
         $responseCode = curl_getinfo($curl, CURLINFO_RESPONSE_CODE);
         if ($response === false || $responseCode != 200) {
-            // log the error?
-            // See curl_error($curl);
+            error_log("Query $verb/$urlPath to labnbook API failed with http code $responseCode: " . curl_error($curl));
             curl_close($curl);
             return $defaultValue;
         }