Initialize ret in safe_printf(...)

../../libasn1print/asn1print.c:59:5: error: ‘ret’ may be used uninitialized in this function [-Werror=maybe-uninitialized]
diff --git a/libasn1print/asn1print.c b/libasn1print/asn1print.c
index 9696dd4..e1e3e48 100644
--- a/libasn1print/asn1print.c
+++ b/libasn1print/asn1print.c
@@ -41,7 +41,7 @@
 
 /* Check printf's error code, to be pedantic. */
 static int safe_printf(const char *fmt, ...) {
-    int ret;
+    int ret = 0;
     va_list ap;
     va_start(ap, fmt);