ox: White spaces after export snippets are never ignored

* lisp/ox.el (org-export-data): White spaces after export snippets are
  never ignored.
* testing/lisp/test-ox.el: Add test.

Back-end developers should pay attention to the fact that white spaces
before and after an ignored export snippet now are accumulated in the
output.

lisp/ox.el

@@ -2062,8 +2062,12 @@ Return transcoded string."
 			 (eq (plist-get info :with-archived-trees) 'headline)
 			 (org-element-property :archivedp data)))
 		(let ((transcoder (org-export-transcoder data info)))
-		  (and (functionp transcoder)
-		       (funcall transcoder data nil info))))
+		  (or (and (functionp transcoder)
+			   (funcall transcoder data nil info))
+		      ;; Export snippets never return a nil value so
+		      ;; that white spaces following them are never
+		      ;; ignored.
+		      (and (eq type 'export-snippet) ""))))
 	       ;; Element/Object with contents.
 	       (t
 		(let ((transcoder (org-export-transcoder data info)))

testing/lisp/test-ox.el

@@ -871,7 +871,16 @@ body\n")))
       (let ((org-export-snippet-translation-alist nil))
 	(should (equal (org-export-as 'test) "A\n")))
       (let ((org-export-snippet-translation-alist '(("t" . "test"))))
-	(should (equal (org-export-as 'test) "AB\n"))))))
+	(should (equal (org-export-as 'test) "AB\n")))))
+  ;; Ignored export snippets do not remove any blank.
+  (should
+   (equal "begin  end\n"
+	  (org-test-with-parsed-data "begin @@test:A@@ end"
+	    (org-export-data-with-translations
+	     tree
+	     '((paragraph . (lambda (paragraph contents info) contents))
+	       (section . (lambda (section contents info) contents)))
+	     info)))))