Only donate term if we're interactive *and* have the terminal

As it turns out otherwise fish would hang when sddm starts it as the login shell.

Belongs to #7842.

src/reader.cpp

@@ -1342,7 +1342,8 @@ void reader_init() {
 
     // Set up our fixed terminal modes once,
     // so we don't get flow control just because we inherited it.
-    if (is_interactive_session()) {
+    if (is_interactive_session() &&
+        getpgrp() == tcgetpgrp(STDIN_FILENO)) {
         term_donate(/* quiet */ true);
     }