Fix NPE when configuration resource does not exist

[gastaldi]

This prevents an NPE to be thrown in tests if a configuration file does not exist

[geoand]

Seems reasonable, but how does this happen?

I mean what test did you run that triggered the NPE?

[gastaldi]

@geoand I mistyped the filename in this snippet:

    @RegisterExtension
    static final QuarkusUnitTest config = new QuarkusUnitTest()
            .setAllowTestClassOutsideDeployment(true)
            .withConfigurationResource("blah.properties");

[geoand]

Underwood, thanks