Fix a race condition in create_dir().

diff --git a/server/request.c b/server/request.c
index a035e16..d7602da 100644
--- a/server/request.c
+++ b/server/request.c
@@ -509,7 +509,7 @@
     if (lstat( name, st ) == -1)
     {
         if (errno != ENOENT) fatal_perror( "lstat %s", name );
-        if (mkdir( name, 0700 ) == -1) fatal_perror( "mkdir %s", name );
+        if (mkdir( name, 0700 ) == -1 && errno != EEXIST) fatal_perror( "mkdir %s", name );
         if (lstat( name, st ) == -1) fatal_perror( "lstat %s", name );
     }
     if (!S_ISDIR(st->st_mode)) fatal_error( "%s is not a directory\n", name );