Throw exception on null/placeholder arrays in TNEF

git-svn-id: https://svn.apache.org/repos/asf/poi/trunk@1877044 13f79535-47bb-0310-9956-ffa450edef68

src/scratchpad/src/org/apache/poi/hmef/attribute/MAPIAttribute.java

          if(isMV || isVL) {
             values = LittleEndian.readInt(inp);
          }
+
+         if (type == Types.NULL && values > 1) {
+            throw new IOException("Placeholder/NULL arrays aren't supported.");
+         }
+
          for(int j=0; j<values; j++) {
             int len = getLength(type, inp);
             byte[] data = IOUtils.safelyAllocate(len, MAX_RECORD_LENGTH);