cont.c: prevent a warning of GCC 12.1

... by assigning a dummy value to the allocated stack.

http://rubyci.s3.amazonaws.com/arch/ruby-master/log/20220613T000004Z.log.html.gz
```
cont.c: In function ‘cont_restore_0.constprop’:
cont.c:1489:28: warning: ‘*sp’ may be used uninitialized [-Wmaybe-uninitialized]
 1489 |                 space[0] = *sp;
      |                            ^~~
```

Also it adds some comments about the hack of dummy stack allocation.

0 files changed, 0 insertions, 0 deletions