ref.as_non_null cause random result about wasm-micro-runtime

[wenyongh]

@peter-jerry-ye thanks for reporting the issue! Please try #3156.

[peter-jerry-ye]

I simplified a bit and got unhandled SIGSEGV with

(module
 (data $string_data "asdf")
 (func $print (import "spectest" "print_i32") (param $i i32))
 (memory $memory (export "memory") 1)
 (type $string (array (mut i8)))
 (func $init
  (local $str (ref null $string))
  (array.new_data $string $string_data (i32.const 0) (i32.const 4)) (local.tee $str)
  (ref.as_non_null) 
  (array.len) (call $print))
 (export "_start" (func $init)))

[peter-jerry-ye]

@wenyongh Thank you for the quick response. I confirm it fixes the problem.