A patch from Prateek Ashtikar for "Issue reported while performing Refund & Void (java.lang.ClassCastException: java.lang.String cannot be cast to java.math.BigDecimal)" https://issues.apache.org/jira/browse/OFBIZ-5927

Change committed in AIMPaymentServices.java.

git-svn-id: https://svn.apache.org/repos/asf/ofbiz/trunk@1647522 13f79535-47bb-0310-9956-ffa450edef68