Support badge +0. It is same effect of disableBadge()

Author: Javen

src/cn/jpush/api/push/model/notification/IosNotification.java

@@ -124,11 +124,7 @@ public Builder incrBadge(int badge) {
                 return this;
             }
 
-            if (badge == 0) {
-                LOG.warn("No action for incrBadge(0)");
-                return this;
-                
-            } else if (badge > 0) {
+            if (badge >= 0) {
                 this.badge = "+" + badge;
             } else {
                 this.badge = "" + badge;

test/cn/jpush/api/push/model/notification/IosNotificationTest.java

@@ -63,6 +63,15 @@ public void testBadge_plus_2() {
         Assert.assertEquals("", json, ios.toJSON());
     }
 
+    @Test
+    public void testBadge_plus_0() {
+        IosNotification ios = IosNotification.newBuilder().incrBadge(0).build();
+        JsonObject json = new JsonObject();
+        json.add("badge", new JsonPrimitive("+0"));
+        json.add("sound", new JsonPrimitive(""));
+        Assert.assertEquals("", json, ios.toJSON());
+    }
+    
     @Test
     public void testBadge_minus_2() {
         IosNotification ios = IosNotification.newBuilder().incrBadge(-2).build();