shell config: only resize if on tty

Resize is only called if stdout is opened. If it is not opened, there is
no TTY to be resized.

The previous configuration calls resize on any login shell through
/etc/profile, which outputs an error messages on shells not on a tty.
(That can occur when using ssh to call a command directly, i.e.
`ssh host echo foo`).

share/modules/nixos-shell-config.nix

@@ -112,8 +112,8 @@ in {
               path = builtins.getEnv "PATH";
             in
             ''
-              # fix terminal size
-              eval "$(resize)"
+              # if terminal with stdout, fix terminal size
+              if [ -t 1 ]; then eval "$(resize)"; fi
 
               ${lib.optionalString (pwd != "") "cd '${pwd}' 2>/dev/null"}
               ${lib.optionalString (term != "") "export TERM='${term}'"}