Issue in looking up event indices in `throw` instruction validation

[takikawa]

I think there is a small bug in validating throw in cases like the following:

(assert_invalid
  (module
    (type (func))     ;; func type at index 0
    (func throw 0))   ;; event at index 0, which is missing
  "throw index out of bounds")

I believe this should be invalid, because the throw argument index should index into the events vector of the module, but it's looking up in the function types vector instead. Currently it doesn't throw an error.

(I can submit a PR to fix this, though maybe I should wait to see if there are thoughts on PR #152 first as it affects catch in that PR too)

[yurydelendik]

I believe this should be invalid, because the throw argument index should index into the events vector of the module

Yes, we need to fail here.

[alexcrichton]

Fixed in #154