ob-latex: Stop ignoring headers argument

lisp/ob-latex.el: During default "png" export, the "headers" argument
is no longer explicitly ignored.

lisp/ob-latex.el

@@ -108,8 +108,11 @@ This function is called by `org-babel-execute-src-block'."
 	      (append (cdr (assq :packages params)) org-latex-packages-alist)))
         (cond
          ((and (string-suffix-p ".png" out-file) (not imagemagick))
-          (org-create-formula-image
-           body out-file org-format-latex-options in-buffer))
+          (let ((org-format-latex-header
+		 (concat org-format-latex-header "\n"
+			 (mapconcat #'identity headers "\n"))))
+	   (org-create-formula-image
+            body out-file org-format-latex-options in-buffer)))
          ((string-suffix-p ".tikz" out-file)
 	  (when (file-exists-p out-file) (delete-file out-file))
 	  (with-temp-file out-file