Variability: Improved check for legal feature names

The Check for legal feature names now also checks that the name is
non-empty.

Issue-ref: 4257
Issue-URL: af3#4257

Signed-off-by: Andreas Bayha <bayha@fortiss.org>

org.fortiss.variability/src/org/fortiss/variability/util/.ratings

 FeatureModelTransformationUtils.java b38702296dcb48ff311b382bb9c05d2590e2dfac GREEN
 Pair.java 2dfd7dc65f7b9ba09a120f1a6058d1e8e9556a37 GREEN
-VariabilityUtils.java 66a727bdb58715dc7b1bd0ce320bd647f374f7d6 GREEN
+VariabilityUtils.java ebb4733f5034f57a73b93160ab25c37d1698c3e2 YELLOW
 VariabilityUtilsInternal.java 9c781a47513bb0c4ddcd13be1c27d62b70f25998 GREEN

org.fortiss.variability/src/org/fortiss/variability/util/VariabilityUtils.java

@@ -170,7 +170,7 @@ public class VariabilityUtils {
 			return false;
 		}
 
-		return literalName.matches(FEATURE_LITERAL_LEGAL_CHAR_REGEX + "*");
+		return literalName.matches(FEATURE_LITERAL_LEGAL_CHAR_REGEX + "+");
 	}
 
 	/**