Failing jpkg test

[Mark Reinhold]

The unit test org/openjdk/jigsaw/cli/JpkgArgsTest.java is failing for me
on a full build of the current Jigsaw forest (linux-i586, though I doubt
it matters).  Log attached below.

It looks like the testIfFileArgIsEmpty method needs to catch and supress
the exception that's thrown, just like the other testIf* methods.

- Mark

--
Test: Check if module path argument exists
Test: Check if module path argument is not a directory
Test: Check if module path argument is not readable
Test: Check if absolute resource path argument is accepted
Test: NPE if file argument does not exist: 
Test: NPE if file argument is not a directory: 
Test: NPE if file argument is not readable: 
Test: IOException if file argument is an empty directory: 
Test: NPE if file argument does not exist:  --config
Test: NPE if file argument is not a directory:  --config
Test: NPE if file argument is not readable:  --config
Test: IOException if file argument is an empty directory:  --config
java.io.IOException: Path is empty: tmp/src/config
	at org.openjdk.jigsaw.ModuleFileFormat$Writer.writeFile(ModuleFileFormat.java:245)
	at org.openjdk.jigsaw.ModuleFileFormat$Writer.writeSection(ModuleFileFormat.java:185)
	at org.openjdk.jigsaw.ModuleFileFormat$Writer.writeOptionalSections(ModuleFileFormat.java:505)
	at org.openjdk.jigsaw.ModuleFileFormat$Writer.writeModule(ModuleFileFormat.java:151)
	at org.openjdk.jigsaw.cli.Packager$Jmod.go(Packager.java:230)
	at org.openjdk.jigsaw.cli.Packager$Jmod.go(Packager.java:171)
	at org.openjdk.jigsaw.cli.Command.run(Command.java:97)
	at org.openjdk.jigsaw.cli.Packager.exec(Packager.java:1112)
	at org.openjdk.jigsaw.cli.Packager.run(Packager.java:856)
	at JpkgArgsTest.compress(JpkgArgsTest.java:345)
	at JpkgArgsTest.testIfFileArgIsEmpty(JpkgArgsTest.java:174)
	at JpkgArgsTest.test(JpkgArgsTest.java:291)
	at JpkgArgsTest.run(JpkgArgsTest.java:47)
	at JpkgArgsTest.main(JpkgArgsTest.java:42)
org.openjdk.jigsaw.cli.Command$Exception: I/O error: Path is empty: tmp/src/config
	at org.openjdk.jigsaw.cli.Packager$Jmod.go(Packager.java:235)
	at org.openjdk.jigsaw.cli.Packager$Jmod.go(Packager.java:171)
	at org.openjdk.jigsaw.cli.Command.run(Command.java:97)
	at org.openjdk.jigsaw.cli.Packager.exec(Packager.java:1112)
	at org.openjdk.jigsaw.cli.Packager.run(Packager.java:856)
	at JpkgArgsTest.compress(JpkgArgsTest.java:345)
	at JpkgArgsTest.testIfFileArgIsEmpty(JpkgArgsTest.java:174)
	at JpkgArgsTest.test(JpkgArgsTest.java:291)
	at JpkgArgsTest.run(JpkgArgsTest.java:47)
	at JpkgArgsTest.main(JpkgArgsTest.java:42)
Caused by: java.io.IOException: Path is empty: tmp/src/config
	at org.openjdk.jigsaw.ModuleFileFormat$Writer.writeFile(ModuleFileFormat.java:245)
	at org.openjdk.jigsaw.ModuleFileFormat$Writer.writeSection(ModuleFileFormat.java:185)
	at org.openjdk.jigsaw.ModuleFileFormat$Writer.writeOptionalSections(ModuleFileFormat.java:505)
	at org.openjdk.jigsaw.ModuleFileFormat$Writer.writeModule(ModuleFileFormat.java:151)
	at org.openjdk.jigsaw.cli.Packager$Jmod.go(Packager.java:230)
	... 9 more
Exception in thread "main" java.lang.Exception: 1/12 tests failed
	at JpkgArgsTest.run(JpkgArgsTest.java:57)
	at JpkgArgsTest.main(JpkgArgsTest.java:42)