Fix off by one error in strtcpy.

The strtcpy function could overrun its output buffer.
diff --git a/src/util.c b/src/util.c
index b89a2b5..bbef995 100644
--- a/src/util.c
+++ b/src/util.c
@@ -262,7 +262,7 @@
 strtcpy(char *dest, const char *src, size_t len)
 {
     char *d = dest;
-    while (len-- && *src != '\0')
+    while (--len && *src != '\0')
         *d++ = *src++;
     *d = '\0';
     return dest;