fix(seo): correct social preview image path inside <meta> tag (#1623)

Author: cotes2020

_includes/img-url.html

@@ -14,24 +14,26 @@
 
 {%- if url -%}
   {% unless url contains ':' %}
-    {%- comment -%} CND URL {%- endcomment -%}
-    {% assign prefix = site.img_cdn | default: '' %}
-
     {%- comment -%} Add page image path prefix {%- endcomment -%}
     {% assign url = include.img_path | default: '' | append: '/' | append: url %}
 
-    {% assign url = prefix
-      | append: '/'
-      | append: url
-      | replace: '///', '/'
-      | replace: '//', '/'
-      | replace: ':', ':/'
-    %}
-
-    {% if include.absolute %}
-      {% assign url = site.url | append: site.baseurl | append: url %}
-    {% else %}
-      {% assign url = site.baseurl | append: url %}
+    {%- comment -%} CND URL {%- endcomment -%}
+    {% if site.img_cdn %}
+      {% assign url = site.img_cdn
+        | append: '/'
+        | append: url
+        | replace: '///', '/'
+        | replace: '//', '/'
+        | replace: ':/', '://'
+      %}
+
+      {% unless site.img_cdn contains ':' %}
+        {% if include.absolute %}
+          {% assign url = site.url | append: site.baseurl | append: url %}
+        {% else %}
+          {% assign url = site.baseurl | append: url %}
+        {% endif %}
+      {% endunless %}
     {% endif %}
   {% endunless %}
 {%- endif -%}