The Guard's Wait-Loop Rule Closes a Loop at a Quoted Separator Before done #2207

Problem

_loop_parts finds a loop's do and done by command position alone and never reads the quote mask. A quoted ";" before a done word therefore reads as a separator, and the loop is closed there, before its real done.

Reproduce (constructed)

Allowed on develop, and bash prints ; done, sleeps, and repeats forever:

while true; do echo ";" done; sleep 1; done

Done looks like

_loop_parts takes the quote mask where it is known and ignores a quoted separator when it looks for do and done. The command above is denied, and a self-test row pins it.

Found by the local strict review of the #2080 fix (handoff #2137). It predates that fix.