add additional exception info to failing IOUtils.toByteArray

git-svn-id: https://svn.apache.org/repos/asf/poi/trunk@1830779 13f79535-47bb-0310-9956-ffa450edef68

src/java/org/apache/poi/util/IOUtils.java

@@ -166,7 +166,7 @@ public final class IOUtils {
         }
 
         if (len != Integer.MAX_VALUE && totalBytes < len) {
-            throw new EOFException("unexpected EOF");
+            throw new EOFException("unexpected EOF - expected len: "+len+" - actual len: "+totalBytes);
         }
 
         return baos.toByteArray();