wallabag : fixes synchronization when "send review as tags" is checked (#8733)

In this PR https://github.com/koreader/koreader/pull/8637
It worked on my sev environnement, but when updating my device, there
were synchronization errors.

Apparently sometimes documents do not have a summary.
To avoid an error during the synchronisation this change adds checks
when getting tags for the document.

plugins/wallabag.koplugin/main.lua

@@ -807,6 +807,7 @@ function Wallabag:addTags(path)
     if id then
         local docinfo = DocSettings:open(path)
 
+        if docinfo.data and docinfo.data.summary and docinfo.data.summary.note then
           local tags = docinfo.data.summary.note
 
           if tags ~= "" and tags ~= nil then
@@ -814,7 +815,7 @@ function Wallabag:addTags(path)
               logger.dbg("Wallabag: sending tags ", tags, " for ", path)
 
               local body = {
-                tags = tags
+                  tags = tags,
               }
 
               local bodyJSON = JSON.encode(body)
@@ -830,7 +831,7 @@ function Wallabag:addTags(path)
           else
               logger.dbg("Wallabag: no tags to send for ", path)
           end
-
+       end
     end
 end