[fix] missing throw in PKey::EC::Point#add

Author: kares

src/main/java/org/jruby/ext/openssl/PKeyEC.java

@@ -1380,7 +1380,7 @@ public IRubyObject add(final ThreadContext context, final IRubyObject other) {
 
             pointResult = pointSelf.add(pointOther);
             if (pointResult == null) {
-                newECError(runtime, "EC_POINT_add");
+                throw newECError(runtime, "EC_POINT_add");
             }
 
             result = new Point(runtime, EC5Util.convertPoint(pointResult), group);