[TEAMMATES#9071] Instructor: enroll students: blank lines processed b…

…y back-end during enrollment [TEAMMATES#9073]

src/main/webapp/dev/js/common/instructorEnroll.js

@@ -39,6 +39,7 @@ function getUserDataRows(spreadsheetData) {
     // needs to check for '' as an initial empty row with null values will be converted to e.g. "||||" after .map
     return spreadsheetData.filter(row => (!row.every(cell => cell === null || cell === '')))
             .map(row => row.join('|'))
+            .map(row => row.replace(/\n|\r/g, ''))
             .join('\n');
 }