fix if statement handling for solc 0.7.0+

[samczsun]

solidity started stripping null members it seems. this might not be the only thing that's broken, but I guess we can fix them as we stumble across them.

repro case:

solc, the solidity compiler commandline interface
Version: 0.7.0+commit.9e61f92b.Linux.g++

contract C {
    function f() public {
        if (0 > 0) {
            0;
        }
    }
}