Rewatch: fix non-unicode stderr (#7613)

Author: cknitt

rewatch/src/build/parse.rs

@@ -332,8 +332,9 @@ fn generate_ast(
             .expect("Error converting .res to .ast"),
     ) {
         Some(res_to_ast) => {
-            let stderr = std::str::from_utf8(&res_to_ast.stderr).expect("Expect StdErr to be non-null");
-            if helpers::contains_ascii_characters(stderr) {
+            let stderr = String::from_utf8_lossy(&res_to_ast.stderr).to_string();
+
+            if helpers::contains_ascii_characters(&stderr) {
                 if res_to_ast.status.success() {
                     Ok((ast_path, Some(stderr.to_string())))
                 } else {