fix error message for when DidChangeTextDocument path doesn't exist

crates/rust-analyzer/src/main_loop.rs

@@ -660,7 +660,7 @@ fn on_notification(&mut self, not: Notification) -> Result<()> {
                             doc.version = params.text_document.version;
                         }
                         None => {
-                            tracing::error!("expected DidChangeTextDocument: {}", path);
+                            tracing::error!("unexpected DidChangeTextDocument: {}; send DidOpenTextDocument first", path);
                             return Ok(());
                         }
                     };