Instead of doing malloc/free every time and "manual" buffer population.
This reuses the dynbuf for this purpose for the duration of parsing the
file.
Closes#18230
When the config file parser detects a word that *probably* should be
quoted, mention double-quotes as a possible remedy.
Test 459 verifies.
Proposed-by: Jiehong on github
Fixes#12409Closes#12412