Bug 1915397 - fix resource leak in MimeMultipartAlternative_flush_children. r=john.bieling

CID: 1537771

Differential Revision: https://phabricator.services.mozilla.com/D223677

--HG--
extra : amend_source : 787cf54c0402a0650700c662978a449f95b08a79

mailnews/mime/src/mimemalt.cpp

@@ -238,6 +238,7 @@ static int MimeMultipartAlternative_flush_children(MimeObject* obj,
                                                    do_display && display_part);
       MimeHeaders_free(malt->buffered_hdrs[i]);
       MimePartBufferDestroy(malt->part_buffers[i]);
+      PR_FREEIF(ct);
     }
     malt->pending_parts = 0;
   }