no longer swallow the phpcr-odm exception

as it only occurs when something really went wrong. the candidates strategy now checks to only try valid paths.

| Q             | A
| ------------- | ---
| Bug fix?      | yes
| New feature?  | no
| BC breaks?    | no
| Deprecations? | no
| Tests pass?   | yes
| Fixed tickets | #143
| License       | MIT
| Doc PR        | -