Fix escaped markdown passing backslashes through

Fixes https://github.com/vector-im/riot-web/issues/11230

Signed-off-by: Bob Rao <bob+git@vulpin.com>

src/editor/serialize.js

@@ -41,6 +41,10 @@ export function htmlSerializeIfNeeded(model, {forceHTML = false} = {}) {
     if (!parser.isPlainText() || forceHTML) {
         return parser.toHTML();
     }
+    // Format "plain" text to ensure removal of backslash escapes
+    // https://github.com/vector-im/riot-web/issues/11230
+    // https://github.com/vector-im/riot-web/issues/2870
+    return parser.toPlaintext();
 }
 
 export function textSerialize(model) {

test/editor/serialize-test.js

@@ -43,4 +43,10 @@ describe('editor/serialize', function() {
         const html = htmlSerializeIfNeeded(model, {});
         expect(html).toBe("<em>hello</em> world");
     });
+    it('escaped markdown should not retain backslashes', function() {
+        const pc = createPartCreator();
+        const model = new EditorModel([pc.plain('\\*hello\\* world')]);
+        const html = htmlSerializeIfNeeded(model, {});
+        expect(html).toBe('*hello* world');
+    })
 });