Make it a fatal error if no source files for Java module.

Change-Id: Ia04158c11381b6b1687b9d5c699a9ea8ae3cb317
diff --git a/core/java_library.mk b/core/java_library.mk
index 67c1bcb..9dbd79b 100644
--- a/core/java_library.mk
+++ b/core/java_library.mk
@@ -18,10 +18,9 @@
 ifneq (,$(LOCAL_RESOURCE_DIR))
 $(error $(LOCAL_PATH): Target java libraries may not set LOCAL_RESOURCE_DIR)
 endif
-endif
-
-#xxx base_rules.mk looks at this
+# base_rules.mk looks at this
 all_res_assets :=
+endif
 
 LOCAL_BUILT_MODULE_STEM := javalib.jar