fix the bug of region filtering

maker/java/src/main/java/org/lionsoul/ip2region/xdb/Maker.java

@@ -178,6 +178,10 @@ public class Maker {
 
                 // apply the field filtering
                 final String region = Util.regionFiltering(seg.region, fields);
+                if (region.length() < 1) {
+                    throw new Exception("empty region info for segment `"+seg+"`");
+                }
+
                 segments.add(new Segment(seg.startIP, seg.endIP, region));
                 last = seg;
             }

maker/java/src/main/java/org/lionsoul/ip2region/xdb/Util.java

@@ -118,7 +118,7 @@ public class Util
             }
 
             sb.append(fs[idx]);
-            if (sb.length() > 0 && i < tailing) {
+            if (i < tailing) {
                 sb.append("|");
             }
         }

maker/java/src/test/java/org/lionsoul/ip2region/xdb/UtilTest.java

@@ -80,7 +80,10 @@ public class UtilTest {
     public void testRegionFiltering() {
         final String[] regions = new String[]{
             "亚洲|中国|广东|深圳|宝安|电信|113.88311|22.55371|440306|0755|518100|Asia/Shanghai|CNY|11|CHXX0120",
-            "大洲|国家|省份|城市|区县|ISP|经度|纬度|0|0|0|0|0"
+            "大洲|国家|省份|城市|区县|ISP|经度|纬度|0|0|0|0|0",
+            "||||||||||||",
+            "亚洲|中国|||||||||||",
+            "美国|加利福尼亚州|洛杉矶|专线用户|||||||||"
         };
 
         final int[] fields = new int[] {1,2,3,4,6,7};