Fail if a product launch configuration cannot be found.

Change-Id: Ide7112cb4bf712047dea33bc723d9ec011a0bcc1
diff --git a/org.eclipse.tea.library.build.lcdsl/src/org/eclipse/tea/library/build/lcdsl/tasks/p2/TaskGenFeatureFromLcDsl.java b/org.eclipse.tea.library.build.lcdsl/src/org/eclipse/tea/library/build/lcdsl/tasks/p2/TaskGenFeatureFromLcDsl.java
index 27b8adc..d1e9e3f 100644
--- a/org.eclipse.tea.library.build.lcdsl/src/org/eclipse/tea/library/build/lcdsl/tasks/p2/TaskGenFeatureFromLcDsl.java
+++ b/org.eclipse.tea.library.build.lcdsl/src/org/eclipse/tea/library/build/lcdsl/tasks/p2/TaskGenFeatureFromLcDsl.java
@@ -133,8 +133,7 @@
 		for (String lcName : dependencies.split(",")) {
 			LaunchConfig lc = LcDslHelper.getInstance().findLaunchConfig(lcName);
 			if (lc == null) {
-				log.info("cannot find launch configuration " + lcName);
-				return Collections.emptyList();
+				throw new IllegalStateException("Cannot find launch configuartion " + lcName);
 			}
 
 			for (Map.Entry<BundleDescription, StartLevel> entry : DependencyResolver.findDependencies(lc, true)