nsh/alias: Fix compiler warning

[wengzhe]

Summary

Got use-after-free warning under GCC 12 with -O3 option, and I found that nsh_strcat may realloc ptr, then cmdline may point to invalid memory.

Let cmdline point to the reallocated ptr may solve the problem. Tested by alias ll='ls -l' and ll / on sim.

GCC output:

CC:  binfmt_unloadmodule.c In function 'nsh_aliasexpand',
    inlined from 'nsh_argument' at nsh_parse.c:1879:20:
nsh_parse.c:1196:23: error: pointer 'ptr' used after 'realloc' [-Werror=use-after-free]
 1196 |               ptr     = cmdline + len;
      |               ~~~~~~~~^~~~~~~~~~~~~~~
In function 'nsh_strcat',
    inlined from 'nsh_aliasexpand' at nsh_parse.c:1190:21,
    inlined from 'nsh_argument' at nsh_parse.c:1879:20:
nsh_parse.c:1100:27: note: call to 'realloc' here
 1100 |   argument  = (FAR char *)realloc(s1, allocsize);
      |                           ^~~~~~~~~~~~~~~~~~~~~~

Impact

nsh alias

Testing

Tested by alias ll='ls -l' and ll / on sim.