org-odt.el: Fix a regression in export of src blocks

* contrib/lisp/org-odt.el
(org-odt-format-source-line-with-line-number-and-label): When
numbering was turned off, src blocks were getting stripped
from export.  Fixed this regression.

contrib/lisp/org-odt.el

@@ -1045,7 +1045,7 @@ to make available an enhanced version of `htmlfontify' library."
     (when ref
       (setq line (org-odt-format-target line (concat "coderef-" ref))))
     (setq line (org-odt-format-stylized-paragraph par-style line))
-    (when num
+    (if (not num) line
       (org-odt-format-tags '("<text:list-item>" . "</text:list-item>") line))))
 
 (defun org-odt-format-source-code-or-example-plain