Remove some code duplication and add a check for a potential error situation in which two feature generators of the same name are registered. This fixes the potential issue where the feature is in _features.json and the mod that added it has made the API calls that originally added it

Author: dshadowwolf

src/main/java/com/mcmoddev/orespawn/data/FeatureRegistry.java

@@ -64,20 +64,20 @@ public boolean hasFeature(String name) {
 	public boolean hasFeature(IFeature feature) {
 		return featuresInverse.containsKey(feature);
 	}
+
 
 	public void addFeature(JsonObject entry) {
-		IFeature feature = getInstance(entry.get("class").getAsString());
-		if( feature != null ) {
-			features.put(entry.get("name").getAsString(), feature);
-			featuresInverse.put(feature, entry.get("name").getAsString());
-		}
+		this.addFeature(entry.get("name").getAsString(), entry.get("class").getAsString());
 	}
 
 	public void addFeature(String name, String className) {
 		IFeature feature = getInstance(className);
 		if( feature != null ) {
-			features.put(name, feature);
-			featuresInverse.put(feature, name);
+			// the feature might already be registered
+			if( !features.containsKey(name) ) {
+				features.put(name, feature);
+				featuresInverse.put(feature, name);
+			}
 		}		
 	}