add additional sanity checks

git-svn-id: https://svn.apache.org/repos/asf/poi/trunk@1142880 13f79535-47bb-0310-9956-ffa450edef68

src/scratchpad/src/org/apache/poi/hwpf/model/BytePropertyNode.java

@@ -38,6 +38,11 @@ public abstract class BytePropertyNode extends PropertyNode {
 				translator.getCharIndex(fcEnd, translator.getCharIndex(fcStart)),
 				buf
 		);
+
+        if ( fcStart > fcEnd )
+            throw new IllegalArgumentException( "fcStart (" + fcStart
+                    + ") > fcEnd (" + fcEnd + ")" );
+
                 this.startBytes = fcStart;
                 this.endBytes = fcEnd;
 	}

src/scratchpad/src/org/apache/poi/hwpf/model/PropertyNode.java

@@ -56,6 +56,10 @@ public abstract class PropertyNode implements Comparable, Cloneable
     	  _logger.log(POILogger.WARN, "A property claimed to start before zero, at " + _cpStart + "! Resetting it to zero, and hoping for the best");
     	  _cpStart = 0;
       }
+
+      if ( fcStart > fcEnd )
+          throw new IllegalArgumentException( "fcStart (" + fcStart
+                  + ") > fcEnd (" + fcEnd + ")" );
   }
 
   /**