[11_39] Render unicode in the cjk font when its range is in latin

Before:

![image](https://github.com/user-attachments/assets/de724cee-ce5a-450a-a621-6c73b665b3f4)


Now:

zh:

![image](https://github.com/user-attachments/assets/2950bf50-97a1-4729-9d41-9d1d0a717cbf)

en:

![image](https://github.com/user-attachments/assets/efba372c-8e01-40be-a91e-b4a14c12e3a1)

en in GNU TeXmacs 2.1.4:

![image](https://github.com/user-attachments/assets/10ca9796-8d94-4a4d-b5e3-ed194674b3d4)



symbl.cc:

![image](https://github.com/user-attachments/assets/cea27151-3451-4233-9a2e-60cf1fce753b)

TeXmacs/tests/tmu/11_39_nbsp.tmu

@@ -0,0 +1,14 @@
+<TMU|<tuple|1.0.5|1.2.9.3>>
+
+<style|<tuple|generic|chinese>>
+
+<\body>
+
+</body>
+
+<\initial>
+  <\collection>
+    <associate|page-medium|paper>
+    <associate|page-screen-margin|false>
+  </collection>
+</initial>

TeXmacs/tests/tmu/11_39_nbsp_2.tmu

@@ -0,0 +1,14 @@
+<TMU|<tuple|1.0.5|1.2.9.3>>
+
+<style|<tuple|generic|chinese>>
+
+<\body>
+  <nbsp>
+</body>
+
+<\initial>
+  <\collection>
+    <associate|page-medium|paper>
+    <associate|page-screen-margin|false>
+  </collection>
+</initial>