erp5_corporate_identity: make sure header list has element before access

bt5/erp5_corporate_identity/SkinTemplateItem/portal_skins/erp5_corporate_identity/WebPage_downgradeHeaders.py

@@ -9,7 +9,9 @@ def pushDown(level):
   return ''.join(["h", str(level), ">"])
 
 for header in re.findall("<h[1-6].*</h[1-6]>", content or ""):
-  tag = re.findall("<(h[1-6]>)", header)[0] #h2>
+  header_list = re.findall("<(h[1-6]>)", header)
+  if len(header_list):
+    tag = header_list[0] #h2>
     key = tag[1]
     content = content.replace(
       header,