binfmt_execmodule: If incoming envp is NULL get parent envp

This keeps backwards compatibility with apps that do not provide
envp. The old implementation passes NULL always and this change fixes
any regression caused by it.

binfmt/binfmt_execmodule.c

@@ -153,7 +153,7 @@ int exec_module(FAR const struct binary_s *binp,
 
   /* Make a copy of the environment here */
 
-  if (envp)
+  if (envp || (envp = get_environ_ptr()))
     {
       envp = binfmt_copyenv(envp);
       if (!envp)