Fix Janino-related NPE in bootstrap class loader

[trask]

I have been using SLF4J/Logback successfully inside the bootstrap class loader for a while now, but recently tried to add conditional processing (Janino) in the logback.xml and ran into a NullPointerException:

        at java.lang.NullPointerException
        at      at ch.qos.logback.core.util.EnvUtil.isJaninoAvailable(EnvUtil.java:59)
        at      at ch.qos.logback.core.joran.conditional.IfAction.begin(IfAction.java:51)
        at      at ch.qos.logback.core.joran.spi.Interpreter.callBeginAction(Interpreter.java:275)
        at      at ch.qos.logback.core.joran.spi.Interpreter.startElement(Interpreter.java:147)
        at      at ch.qos.logback.core.joran.spi.Interpreter.startElement(Interpreter.java:129)
        at      at ch.qos.logback.core.joran.spi.EventPlayer.play(EventPlayer.java:50)
        at      at ch.qos.logback.core.joran.GenericConfigurator.doConfigure(GenericConfigurator.java:149)
        at      at ch.qos.logback.core.joran.GenericConfigurator.doConfigure(GenericConfigurator.java:135)
        at      at ch.qos.logback.core.joran.GenericConfigurator.doConfigure(GenericConfigurator.java:99)
        at      at ch.qos.logback.core.joran.GenericConfigurator.doConfigure(GenericConfigurator.java:49)
        at      at ch.qos.logback.classic.util.ContextInitializer.configureByResource(ContextInitializer.java:77)
        at      at ch.qos.logback.classic.util.ContextInitializer.autoConfig(ContextInitializer.java:152)
        at      at org.slf4j.impl.StaticLoggerBinder.init(StaticLoggerBinder.java:85)
        at      at org.slf4j.impl.StaticLoggerBinder.<clinit>(StaticLoggerBinder.java:55)
        at      at org.slf4j.LoggerFactory.bind(LoggerFactory.java:140)
        at      at org.slf4j.LoggerFactory.performInitialization(LoggerFactory.java:119)
        at      at org.slf4j.LoggerFactory.getILoggerFactory(LoggerFactory.java:328)
        at      at org.slf4j.LoggerFactory.getLogger(LoggerFactory.java:280)
        at      at org.slf4j.LoggerFactory.getLogger(LoggerFactory.java:301)

I hope you will accept this one-line fix to resolve the issue.

Thanks, Trask