SI-6158 Restore compile error output under partest --show-log

Seems like the ifs and elses didn't quite survive e830a7ce9.

Before:

    ./test/partest --show-log test/files/run/foo.scala
    Testing individual files
    testing: [...]/files/run/foo.scala                                    [FAILED]

Now:

    ./test/partest --show-log test/files/run/foo.scala
    Testing individual files
    testing: [...]/files/run/foo.scala                                    [FAILED]
    foo.scala:1: error: expected class or object definition
    askdfjskl
    ^
    one error found
    1 of 1 tests failed (elapsed time: 00:00:01)
Merge pull request #2099 from retronym/ticket/6158

SI-6158 Restore compile error output under partest --show-log