Fix word_id in 25-persistent-tables

"MAX(id) FROM words" was used as word_id for INSERT of next word,
which will result in duplicate word ids.

(Of course, in its current form, the application always runs the code against
an empty database, so the error is not triggered.)

Author: tingstad

25-persistent-tables/tf-25.py

@@ -37,9 +37,7 @@ def _extract_words(path_to_file):
     # Add the words to the database
     c.execute("SELECT MAX(id) FROM words")
     row = c.fetchone()
-    word_id = row[0]
-    if word_id == None:
-        word_id = 0
+    word_id = row[0] + 1 if row[0] != None else 0
     for w in words:
         c.execute("INSERT INTO words VALUES (?, ?, ?)", (word_id, doc_id, w))
         # Add the characters to the database