Fix constructor call if no constructor exist

[montyly]

This PR fixes when this happens:

contract A{ constructor(uint) }
contract B is A {}
contract C is B{ constructor() A(10) B() {}

C calls B(), which does not exist. Slither incorrectly took A.constructor as the call's target.

This is a quick fix, a long term solution would be to check for the constructor's signature. Unfortunately, this information is not yet created when the conversion is done; the correct fix will require more work.