Stack position may be bigger than stack bottom; fix
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MODIFY
src/vm.c
src/vm.c
@@ -137,6 +137,7 @@ stack_extend_alloc(mrb_state *mrb, int room, int keep)
size_t size = mrb->c->stend - mrb->c->stbase;
size_t off = mrb->c->stack - mrb->c->stbase;
+ if (off > size) size = off;
#ifdef MRB_STACK_EXTEND_DOUBLING
if (room <= size)
size *= 2;

Stack position may be bigger than stack bottom; fix #3401

This issue was reported by https://hackerone.com/titanous