Fix default impl of Escape::escape_to_buf and add a simple test case for EscapeJsonString

sailfish-tests/integration-tests/templates/json_escape.out

@@ -0,0 +1,3 @@
+{
+    "name": "Dwayne \"The Rock\" Johnson"
+}

sailfish-tests/integration-tests/templates/json_escape.stpl

@@ -0,0 +1,3 @@
+{
+    "name": "<%\json &self.name %>"
+}

sailfish-tests/integration-tests/tests/template.rs

@@ -85,6 +85,22 @@ fn json() {
     );
 }
 
+#[derive(Render)]
+#[template(path = "json_escape.stpl")]
+struct JsonEscape {
+    name: String,
+}
+
+#[test]
+fn json_escape() {
+    assert_render(
+        "json_escape",
+        JsonEscape {
+            name: String::from(r#"Dwayne "The Rock" Johnson"#),
+        },
+    );
+}
+
 #[derive(Render)]
 #[template(path = "custom_delimiter.stpl")]
 #[template(delimiter = '🍣')]

sailfish/src/escape.rs

@@ -89,6 +89,7 @@ pub trait Escape: const EscapeMeta {
                 i = j + c.len_utf8();
             }
         }
+        buffer.push_str(&string[i..]);
     }
 
     /// Writes the `string` to the `buffer`, applying any necessary escaping.