Spurious 'if block ends with a return statement…' when some preceding if-else clauses don't return unconditionally.

[marcelocantos]

The following expression is flagged by golint, but requires the final else:

$ golint -min_confidence 0 ./jsonnet
jsonnet/cmd.go:324:11: if block ends with a return statement, so drop this else and outdent its block

golint should verify that all preceding if and if else blocks return unconditionally, not just the immediately preceding one.

[marcelocantos]

It turns out the intended behaviour was to ignore if else chains. However, it was returning from ignored IfStmt nodes before checking whether their else node was also an IfStmt. Consequently, the check would fail for an even number of if else blocks. Fixed by #383