nshlib/pipeline: Concat variable arguments failed

1. Without this patch

  nsh> set var_test `uname`
  nsh> echo $var_test
  NuttX
  nsh> echo $var_test | cat
  sh [5:100]

  nsh>

2. With this patch

  nsh> set var_test `uname`
  nsh> echo $var_test
  NuttX
  nsh> echo $var_test | cat
  sh [4:100]
  NuttX
  nsh>

Signed-off-by: wangjianyu3 <wangjianyu3@xiaomi.com>

nshlib/nsh_parse.c

@@ -2677,6 +2677,7 @@ static int nsh_parse_command(FAR struct nsh_vtbl_s *vtbl, FAR char *cmdline)
         {
           FAR char *arg;
           FAR char *sh_argv[4];
+          char sh_arg2[CONFIG_NSH_LINELEN];
 
           if (argv[argc][g_pipeline1_len])
             {
@@ -2694,20 +2695,21 @@ static int nsh_parse_command(FAR struct nsh_vtbl_s *vtbl, FAR char *cmdline)
               goto dynlist_free;
             }
 
-          for (ret = 0; ret < argc - 1; ret++)
-            {
-              FAR char *p_arg = argv[ret];
-              size_t len = strlen(p_arg);
+          sh_arg2[0] = '\0';
 
-              /* Restore from split args to concat args. */
+          for (ret = 0; ret < argc; ret++)
+            {
+              strlcat(sh_arg2, argv[ret], sizeof(sh_arg2));
 
-              DEBUGASSERT(&p_arg[len + 1] == argv[ret + 1]);
-              p_arg[len] = ' ';
+              if (ret < argc - 1)
+                {
+                  strcat(sh_arg2, " ");
+                }
             }
 
           sh_argv[0] = "sh";
           sh_argv[1] = "-c";
-          sh_argv[2] = argv[0];
+          sh_argv[2] = sh_arg2;
           sh_argv[3] = NULL;
 
           ret = pipe2(pipefd, 0);