Pages with an invisible control character now save

Some pages carried an invisible control character in their text. The database cannot store that character at all, so saving those pages failed — and the error said only that something was wrong, without naming the page, the field, or the character, which made it almost impossible to track down.

The two places that produced the character have been fixed, so the pages save normally again. If content ever does contain a character that genuinely cannot be stored, the save now stops before anything is written and reports exactly which page and which field to correct, instead of failing part-way through a batch and leaving you to guess. Nothing is silently trimmed or rewritten to make it fit.