Fix *xattr decoding

* file.c (print_xattr_val): Do not attempt to decode a zero sized array.
Fixes RH#885233.
diff --git a/file.c b/file.c
index b952e7f..1cd8d3c 100644
--- a/file.c
+++ b/file.c
@@ -2466,6 +2466,8 @@
 		unsigned long insize,
 		unsigned long size)
 {
+	if (insize == 0)
+		failed = 1;
 	if (!failed) {
 		unsigned long capacity = 4 * size + 1;
 		unsigned char *buf = (capacity < size) ? NULL : malloc(capacity);