Buffer underflow with empty zip entry names

zip_entry.c has a buffer underflow when a zip entry name is 0-length. It unilaterally checks for a slash at the end of the name, and if the name is empty, it checks at offset -1. Fix:


--- a/src/java.base/share/native/libzip/zip_util.c Thu May 07 10:19:34 2015 -0700
+++ b/src/java.base/share/native/libzip/zip_util.c Fri May 08 10:52:58 2015 -0700
@@ -1206,7 +1206,7 @@
         }
 
         /* Slash is already there? */
- if (name[ulen-1] == '/') {
+ if (ulen > 0 && name[ulen - 1] == '/') {
             break;
         }