Fix passwd seg fault

Passing the -stdin arg to the passwd command line app *and* supply a
password on the command line causes a seg fault.

Reviewed-by: Richard Levitte <levitte@openssl.org>

apps/passwd.c

@@ -175,6 +175,7 @@ int passwd_main(int argc, char **argv)
             if (pw_source_defined)
                 goto opthelp;
             in_stdin = 1;
+            pw_source_defined = 1;
             break;
         }
     }