The definition of strncpy() is that empty space should be zero-filled, the patch adds the zero filling (I didn’t know this, see e.g. the POSIX spec here: http://pubs.opengroup.org/onlinepubs/7908799/xsh/strncpy.html). From Lorenz Meier.

libc/string/lib_strncpy.c

@@ -55,7 +55,8 @@ char *strncpy(FAR char *dest, FAR const char *src, size_t n)
   char *ret = dest;     /* Value to be returned */
   char *end = dest + n; /* End of dest buffer + 1 byte */
 
-  while (dest != end && (*dest++ = *src++) != '\0');
+  while ((*dest++ = *src++) != '\0' && dest != end);
+  while (dest != end) *dest++ = '\0';
   return ret;
 }
 #endif