Fix in codegen for inlined sequence nodes. For inlined sequence nodes, generate nested ifs rather than sequential code which does not work when inlined. The reason is that #codeReturn: in inline generates instvar assignment, not method return, so in sequential code the next child of a sequence will be probed even if previous failed. If that happends, the whole sequence fail and therefore we must generate nested ifs to correctly handle this w.r.t. inlining.