Remove redundant check in zmemzero().

zutil.c

diff --git a/zutil.c b/zutil.c
index 4ea02a9..0e30c56 100644
--- a/zutil.c
+++ b/zutil.c
@@ -171,7 +171,6 @@
 
 void ZLIB_INTERNAL zmemzero(void FAR *b, z_size_t len) {
     uchf *p = b;
-    if (len == 0) return;
     while (len) {
         *p++ = 0;
         len--;