[hackers] [st] Fix style in execsh || Roberto E. Vargas Caballero

[git]

commit 62756fdb4945a80f4a53e6d354d5d93f51035517
Author:     Roberto E. Vargas Caballero <k...@shike2.com>
AuthorDate: Fri Jul 24 07:44:34 2015 +0200
Commit:     Roberto E. Vargas Caballero <k...@shike2.com>
CommitDate: Fri Jul 24 07:44:34 2015 +0200

    Fix style in execsh

diff --git a/st.c b/st.c
index 64e2cec..b604f0e 100644
--- a/st.c
+++ b/st.c
@@ -1329,9 +1329,8 @@ execsh(void)
                        die("who are you?\n");
        }
 
-       if (!(sh = getenv("SHELL"))) {
+       if ((sh = getenv("SHELL")) == NULL)
                sh = (pw->pw_shell[0]) ? pw->pw_shell : shell;
-       }
 
        if (opt_cmd)
                prog = opt_cmd[0];