Don't replace tilde for error messages if we have no $HOME

This was an issue with "--no-execute", which has no variables and
therefore no $HOME:

```fish
fish --no-execute /path/to/file
```

would say the error is in `~/path/to/file`.

Instead, since this is just for a message, we simply return the
filename without doing the replacement.

Fixes #10171

fish-rust/src/expand.rs

@@ -307,6 +307,11 @@ pub fn replace_home_directory_with_tilde(s: &wstr, vars: &dyn Environment) -> WS
     if result.starts_with("/"L) {
         let mut home_directory = "~"L.to_owned();
         expand_tilde(&mut home_directory, vars);
+        // If we can't get a home directory, don't replace anything.
+        // This is the case e.g. with --no-execute
+        if home_directory.is_empty() {
+            return result;
+        }
         if !home_directory.ends_with("/"L) {
             home_directory.push('/');
         }

tests/checks/no-execute.fish

@@ -23,5 +23,14 @@ echo "begin; echo oops" | $fish -n
 echo $status
 #CHECK: 127
 
+echo "begin" > broken
+$fish -n $PWD/broken
+#CHECKERR: /{{.*}}broken (line 1): Missing end to balance this begin
+#CHECKERR: begin
+#CHECKERR: ^~~~^
+#CHECKERR: warning: Error while reading file /{{.*}}broken
+
+rm broken
+
 # Littlecheck assumes a status of 127 means the shebang was invalid.
 exit 0