Assemblyscript sendMessage should fail if target function does not exists

[peterjah]

When using smart contract vm function sendMessage() to schedule a future SC call, targeting a function on a contract that does not exists or targeting a function that is not exported by the contract should fail.
Today, the function is executed and nothing happen (as expected).

Expected behavior
When target contract does not exists, sendMessage() should fail
When target function that is not exported by the target contract , sendMessage() should fail as well with a appropriate error message