Running uncompilable scripts throws NullPointerException

Fix for JDK-8046014 removes the null-check for the script class in Context.getProgramFunction(), causing a NullPointerException down the line for scripts that fail to compile:

Exception in thread "main" java.lang.NullPointerException
at java.lang.invoke.MethodHandles$Lookup.checkSymbolicClass(MethodHandles.java:1390)
at java.lang.invoke.MethodHandles$Lookup.resolveOrFail(MethodHandles.java:1373)
at java.lang.invoke.MethodHandles$Lookup.findStatic(MethodHandles.java:774)
at jdk.nashorn.internal.runtime.Context.getCreateProgramFunctionHandle(Context.java:1025)
at jdk.nashorn.internal.runtime.Context.getProgramFunction(Context.java:1020)
at jdk.nashorn.internal.runtime.Context.compileScript(Context.java:1042)
at jdk.nashorn.internal.runtime.Context.compileScript(Context.java:520)
at jdk.nashorn.tools.Shell.runScripts(Shell.java:314)
at jdk.nashorn.tools.Shell.run(Shell.java:169)
at jdk.nashorn.tools.Shell.main(Shell.java:133)
at jdk.nashorn.tools.Shell.main(Shell.java:112)