Fix error from ceylon/ceylon-spec#891
Fix error from ceylon/ceylon-spec#891

The second `if` no longer narrows the type, so use an else instead.

jeancharles-roger/ceylon-sdk,ASzc/ceylon-sdk,jeancharles-roger/ceylon-sdk,matejonnet/ceylon-sdk,rohitmohan96/ceylon-sdk,ASzc/ceylon-sdk