Check calldatasize before loading func selector

[charles-cooper]

What I did

Fix #1603

How I did it

Implemented the solution from #1603 (comment)

How to verify it

Check tests, also look at IR of following code:

@public
@payable
def blockHashAskewLimitary(v: uint256): # function selector: 0x00000000
  send(msg.sender, self.balance)

@public
def __default__() -> uint256:
  return 1`

Description for the changelog

Fix edge case in function selector with 0 calldata

Cute Animal Picture

[fubuloubu]

Adding my own approval, and referencing OP's approval from #1603 (comment)

[davesque]

Mostly looks good. Left a couple of suggestions for adding comments.

[davesque]

Would be nice to add a note about why this is here. To someone reading the code who's not familiar with the discussion, it might look mysterious.

[davesque]

Can you include the deletion of this constant in a separate commit with a message that explains why it was removed? I had to do a bit of poking around to figure out why this was taken out. It looks like it just wasn't used anymore?

[charles-cooper]

yeah i discovered it was dead code. i can split it into a separate commit

[charles-cooper]

Actually I remember why I put it in the same commit, it's because it had duplicated code with STORE_CALLDATA and I didn't want the commit to change one of the calldataload without changing the other one.

[charles-cooper]

I added a note to the commit message to clarify.