org-html-src-block: Treat code blocks without LANG equally

* lisp/ox-html.el (org-html-src-block): Do not treat src blocks
without LANG as example blocks.  Instead, export them using "nil"
language.  This way, such src blocks will get captions, unlike example
blocks.

The new behavior is consistent with ox-latex and ox-ascii.

Reported-by: Johan Bolmsjö <org-mode@johan.bitmaster.se>
Link: https://orgmode.org/list/87zgb90win.fsf@localhost

lisp/ox-html.el

@@ -3616,7 +3616,6 @@ contextual information."
 	   (klipsify  (and  (plist-get info :html-klipsify-src)
                             (member lang '("javascript" "js"
 					   "ruby" "scheme" "clojure" "php" "html")))))
-      (if (not lang) (format "<pre class=\"example\"%s>\n%s</pre>" label code)
       (format "<div class=\"org-src-container\">\n%s%s\n</div>"
 	      ;; Build caption.
 	      (let ((caption (org-export-get-caption src-block)))
@@ -3634,14 +3633,15 @@ contextual information."
 	      ;; Contents.
 	      (if klipsify
 		  (format "<pre><code class=\"src src-%s\"%s%s>%s</code></pre>"
-			    lang
+			  lang ; lang being nil is OK.
 			  label
 			  (if (string= lang "html")
 			      " data-editor-type=\"html\""
 			    "")
 			  code)
 		(format "<pre class=\"src src-%s\"%s>%s</pre>"
-                          lang label code)))))))
+                        ;; Lang being nil is OK.
+                        lang label code))))))
 
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