fix(ssr): hydration for transition wrapper components with empty slot content (#5995)

fix #5991

packages/server-renderer/__tests__/ssrSlot.spec.ts

@@ -113,4 +113,32 @@ describe('ssr: slot', () => {
       `<div><!--[--><!--[--><div>one</div><div>two</div><!--]--><!--]--></div>`
     )
   })
+
+  test('transition slot', async () => {
+    expect(
+      await renderToString(
+        createApp({
+          components: {
+            one: {
+              template: `<transition><slot/></transition>`
+            }
+          },
+          template: `<one><div v-if="false">foo</div></one>`
+        })
+      )
+    ).toBe(`<!---->`)
+
+    expect(
+      await renderToString(
+        createApp({
+          components: {
+            one: {
+              template: `<transition><slot/></transition>`
+            }
+          },
+          template: `<one><div v-if="true">foo</div></one>`
+        })
+      )
+    ).toBe(`<div>foo</div>`)
+  })
 })