Return line 0 for JIT frames

Frames pushed by YJIT have an unreliable PC.  The PC could be garbage,
and if we try to read the line number with a garbage PC, then the
program can crash.

This commit returns line 0 for programs where there is a `jit_return`
function.  If `jit_return` has been set then this frame was pushed by
the JIT, and we cannot trust the PC.

Here is a debugger session for a program that crashed due to a broken
PC:

```
(lldb) p ruby_current_vm_ptr->ractor.main_thread->ec->cfp->iseq->body->iseq_encoded
(VALUE *) $0 = 0x0000000118a30e00
(lldb) p/x ruby_current_vm_ptr->ractor.main_thread->ec->cfp->pc
(const VALUE *) $1 = 0x0000600000b02d00
(lldb) p/x ruby_current_vm_ptr->ractor.main_thread->ec->cfp->jit_return
(void *) $2 = 0x000000010622942c
```

You can see the PC is completely out of range, but there is a
`jit_return` pointer so we can avoid this crash.

0 files changed, 0 insertions, 0 deletions