drawImplicit: Avoid modifying list during iteration
It's not safe to append to a QList while it's being iterated, because it might get realloc'd.
There's a corner case of drawImplicit where the 'singular' list is modified in an iteration loop, in at least some of those cases (when tan() is used) a crash happens due to that realloc and the iteration using the old data.
Fix by placing the new points on a separate list, and wrapping the loop by an outer loop which iterates until we don't add to the extra list.
BUGS: 426025, 435186