EEI: create should clear the return data buffer on success

[axic]

No description provided.

[axic]

@lrettig @jwasinger @hugo-dc having a test case for this would be nice:

• do a call which fills the return buffer
• do a successful create
• ensure returndatasize equals to 0

A few more combinations :)

[jwasinger]

ensure returndatasize equals to 0

@axic I'm assuming that you mean to inspect the returndatabuffer to ensure it was zeroed out. Otherwise the proposed test case is just testing the behavior of the environment which is already covered by existing state tests.

so the test case would look like this:

   do CALL which fills returndata buffer....
   let l = length(RETURNDATASIZE)
   do CREATE which zeroes returndata buffer....
   assert(mem[returnBuffer:returnBuffer+l] == '0x00000....')

**EDIT** ah maybe I misunderstand how the `returndatabuffer` works.   It is not automatically filled with return data.  It is just the location where return data goes after calling `returndatacopy`

[axic]

Actually the only thing which matters is that returndatasize returns 0, because returndatacopy will throw if someone tries to read more than what's inside (= returndatasize).

Note: I am talking here about getReturnDataSize and returnDataCopy, in all these tests resultOffset and resultLength should both be zero as they are obsolete and to be removed soon. See ewasm/design#70

[jwasinger]

I really would like to have a strong argument for why we can't run state tests transcompiled to eWASM to address cases like this...

I'm not opposed to writing test cases but I feel like we are re-inventing the wheel here