Bob Nystrom
4d413f3473
The crash occurred in captureUpvalue() when an upvalue for an earlier local
variable was captured after a later one. The function walked to the end of the
open upvalue list but then dereferenced a NULL pointer when comparing
upvalue->value against the target local slot.
Added a NULL guard before the equality check so that if no existing upvalue
is found, the function correctly proceeds to create a new one instead of
dereferencing a null pointer.
Also fixed a typo in the comment ("existsing" -> "existing").
Added regression test close_over_later_variable.wren that exercises the
scenario of capturing upvalues for locals in reverse declaration order.