unix: don't close inherited fds on uv_spawn() fail

The cleanup-after-error code path in uv_spawn() was closing file
descriptors indiscriminately.  Only close file descriptors that we
created ourselves, not the ones that are passed in by the user.

Fixes nodejs/node-v0.x-archive#6297.

src/unix/process.c

@@ -186,7 +186,7 @@ int uv__make_pipe(int fds[2], int flags) {
 
 /*
  * Used for initializing stdio streams like options.stdin_stream. Returns
- * zero on success.
+ * zero on success. See also the cleanup section in uv_spawn().
  */
 static int uv__process_init_stdio(uv_stdio_container_t* container, int fds[2]) {
   int mask;
@@ -465,8 +465,13 @@ int uv_spawn(uv_loop_t* loop,
 
   if (pipes != NULL) {
     for (i = 0; i < stdio_count; i++) {
-      close(pipes[i][0]);
-      close(pipes[i][1]);
+      if (i < options.stdio_count)
+        if (options.stdio[i].flags & (UV_INHERIT_FD | UV_INHERIT_STREAM))
+          continue;
+      if (pipes[i][0] != -1)
+        close(pipes[i][0]);
+      if (pipes[i][1] != -1)
+        close(pipes[i][1]);
     }
     free(pipes);
   }