Fix for 37341

cache of filterHash must also be invalidated if a file is read, not only if a single filter is added.

git-svn-id: https://svn.apache.org/repos/asf/ant/core/trunk@330652 13f79535-47bb-0310-9956-ffa450edef68

WHATSNEW

@@ -66,6 +66,8 @@ Changes that could break older environments:
 
 Fixed bugs:
 -----------
+* Problem when adding multiple filter files, Bugzilla Report 37341
+
 * problem refering jars specfied by Class-Path attribute in manifest
   of a ant task jar file, when this ant task jar file is located in
   a directory with space, Bugzilla Report 37085