newdb: Handle damaged one-one text tables

Ignore text records in the database that are damaged, instead of erroring
out. Lets the rest of the data be used. Fixes #1215981 [calibre 1.0 can't find database](https://bugs.launchpad.net/calibre/+bug/1215981)

src/calibre/db/tables.py

@@ -92,7 +92,14 @@ class OneToOneTable(Table):
         query = db.conn.execute('SELECT {0}, {1} FROM {2}'.format(idcol,
             self.metadata['column'], self.metadata['table']))
         if self.unserialize is None:
+            try:
                 self.book_col_map = dict(query)
+            except UnicodeDecodeError:
+                # The db is damaged, try to work around it by ignoring
+                # failures to decode utf-8
+                query = db.conn.execute('SELECT {0}, cast({1} as blob) FROM {2}'.format(idcol,
+                    self.metadata['column'], self.metadata['table']))
+                self.book_col_map = {k:bytes(val).decode('utf-8', 'ignore') for k, val in query}
         else:
             us = self.unserialize
             self.book_col_map = {book_id:us(val) for book_id, val in query}