Disarms a tool: releases exclusive mode and, when armToolCursor painted a cursor,
restores what the map showed before it.
Safe to call when nothing was armed, or when the tool armed without a cursor: the cursor
is then left untouched — a disarm only undoes what an arm painted.
Disarms a tool: releases exclusive mode and, when armToolCursor painted a cursor, restores what the map showed before it.
Safe to call when nothing was armed, or when the tool armed without a cursor: the cursor is then left untouched — a disarm only undoes what an arm painted.