check if a value is a Number before casting

- In some rare cases when generating the JSON diff for a given key, it is possible that the new value is not a number while the old value is an Integer.

- While I can't think of a particular key that can have either an int or string value, crashes have been reported.

- Let's check the old value to be of type Number, maybe it could be a float/double before serialization.

Author: nan-li

OneSignalSDK/onesignal/src/main/java/com/onesignal/JSONUtils.java

@@ -62,7 +62,7 @@ else if (includeFields != null && includeFields.contains(key))
                         Object curValue = cur.get(key);
                         if (!value.equals(curValue)) {
                             // Work around for JSON serializer turning doubles/floats into ints since it drops ending 0's
-                            if (curValue instanceof Integer && !"".equals(value)) {
+                            if (curValue instanceof Number && value instanceof Number) {
                                 if ( ((Number)curValue).doubleValue() != ((Number)value).doubleValue())
                                     output.put(key, value);
                             }