Null check to fix bug 2859588: NullPointerException in
JarJDKToolsLibrary.guessVersion(JarJDKToolsLibrary.java:215)
I'm guessing this is because a zip file was specified as tools.jar location, not a jar file.
M src/edu/rice/cs/drjava/model/JarJDKToolsLibrary.java
Authored by: mgricken 2009-09-15
Parent: [r5068]
Child: [r5070]
