Fix ui test blessing when a test has an empty stderr file after having had content there before the current changes

Author: oli-obk

src/tools/compiletest/src/runtest.rs

@@ -3338,6 +3338,10 @@ impl<'test> TestCx<'test> {
     }
 
     fn delete_file(&self, file: &PathBuf) {
+        if !file.exists() {
+            // Deleting a nonexistant file would error.
+            return;
+        }
         if let Err(e) = fs::remove_file(file) {
             self.fatal(&format!("failed to delete `{}`: {}", file.display(), e,));
         }
@@ -3400,7 +3404,7 @@ impl<'test> TestCx<'test> {
         let examined_content =
             self.load_expected_output_from_path(&examined_path).unwrap_or_else(|_| String::new());
 
-        if examined_path.exists() && canon_content == &examined_content {
+        if canon_content == &examined_content {
             self.delete_file(&examined_path);
         }
     }