fix(koreader): allow plugin API to reset read status to unread

The catalog read-status enum omitted unread, so a device write could only
be undone from the web dashboard. Add it to the settable enum and the
plugin status dialog, and mark Unread as current when a book has no
status row.

Closes #853

koreader-plugin/bookorbit.koplugin/bookorbit_catalog_detail.lua

@@ -708,10 +708,13 @@ end
 function CatalogDetail:showSetStatusDialog(detail)
     local dialog
     local buttons = {}
+    -- A book with no status row comes back with readStatus nil, which the header
+    -- already renders as Unread. Fold it here too so the Unread row is marked.
+    local current = detail.readStatus or "unread"
     for _, status in ipairs(SETTABLE_READ_STATUSES) do
         table.insert(buttons, {
             {
-                text = status.text .. (detail.readStatus == status.id and " *" or ""),
+                text = status.text .. (current == status.id and " *" or ""),
                 callback = function()
                     UIManager:close(dialog)
                     self:applyReadStatus(detail, status.id)

koreader-plugin/bookorbit.koplugin/bookorbit_catalog_util.lua

@@ -84,6 +84,7 @@ CatalogUtil.READ_STATUS_LABELS = {
 -- Read statuses the user can set from the catalog detail page. Kept in sync
 -- with the server's manual read-status enum.
 CatalogUtil.SETTABLE_READ_STATUSES = {
+    { id = "unread", text = _("Unread") },
     { id = "want_to_read", text = _("To read") },
     { id = "reading", text = _("Reading") },
     { id = "on_hold", text = _("On hold") },