Calibre Metadata: Make sure self.books is always flagged as a JSON array

Ditto for self.driveinfo

plugins/calibre.koplugin/metadata.lua

@@ -77,10 +77,10 @@ end
 local CalibreMetadata = {
     -- info about the library itself. It should
     -- hold a table with the contents of "driveinfo.calibre"
-    drive = {},
+    drive = rapidjson.array({}),
     -- info about the books in this library. It should
     -- hold a table with the contents of "metadata.calibre"
-    books = {},
+    books = rapidjson.array({}),
 }
 
 --- loads driveinfo from JSON file
@@ -113,12 +113,12 @@ function CalibreMetadata:loadBookList()
     local attr = lfs.attributes(self.metadata)
     if not attr then
         logger.warn("Unable to get file attributes from JSON file:", self.metadata)
-        return {}
+        return rapidjson.array({})
     end
     local valid = attr.mode == "file" and attr.size > 0
     if not valid then
         logger.warn("File is invalid", self.metadata)
-        return {}
+        return rapidjson.array({})
     end
     local books, err
     local impl = G_reader_settings:readSetting("calibre_json_parser") or attr.size > MAX_JSON_FILESIZE and "safe" or "fast"
@@ -132,7 +132,7 @@ function CalibreMetadata:loadBookList()
     if not books then
         logger.warn(string.format("Unable to load library from json file %s: \n%s",
             self.metadata, err))
-        return {}
+        return rapidjson.array({})
     end
     return books
 end
@@ -141,7 +141,7 @@ end
 function CalibreMetadata:saveBookList()
     local file = self.metadata
     local books = self.books
-    rapidjson.dump(rapidjson.array(books), file, { pretty = true })
+    rapidjson.dump(books, file, { pretty = true })
 end
 
 -- add a book to our books table
@@ -221,8 +221,8 @@ end
 
 -- cleans all temp data stored for current library.
 function CalibreMetadata:clean()
-    self.books = {}
-    self.drive = {}
+    self.books = rapidjson.array({})
+    self.drive = rapidjson.array({})
     self.path = nil
     self.driveinfo = nil
     self.metadata = nil