Make fish_indent stop panicing on closed stdin

Prior to this commit, this code:

    fish_indent <&-

would panic as we would construct a File with a negative fd.
Check for a closed fd as other builtins do.

src/builtins/fish_indent.rs

@@ -1042,6 +1042,13 @@ enum OutputType {
                 ));
                 return Err(STATUS_CMD_ERROR);
             }
+            if streams.stdin_fd < 0 {
+                let cmd = "fish_indent";
+                streams
+                    .err
+                    .append(&wgettext_fmt!("%s: stdin is closed\n", cmd));
+                return Err(STATUS_CMD_ERROR);
+            }
             use std::os::fd::FromRawFd;
             let mut fd = unsafe { std::fs::File::from_raw_fd(streams.stdin_fd) };
             let mut buf = vec![];

tests/checks/indent.fish

@@ -652,3 +652,7 @@ cat $tmpdir/indent_test.fish
 # See that the builtin can be redirected
 printf %s\n a b c | builtin fish_indent | grep b
 # CHECK: b
+
+# Regression test that fish_indent doesn't panic with closed stdin.
+fish_indent <&-
+# CHECKERR: fish_indent: stdin is closed