do not count words when in reverse-only mode

nominatim/tokenizer/icu_tokenizer.py

@@ -99,6 +99,7 @@ class LegacyICUTokenizer(AbstractTokenizer):
         """ Recompute frequencies for all name words.
         """
         with connect(self.dsn) as conn:
+            if conn.table_exists('search_name'):
                 with conn.cursor() as cur:
                     cur.drop_table("word_frequencies")
                     LOG.info("Computing word frequencies")

nominatim/tokenizer/legacy_tokenizer.py

@@ -190,6 +190,7 @@ class LegacyTokenizer(AbstractTokenizer):
         """ Recompute the frequency of full words.
         """
         with connect(self.dsn) as conn:
+            if conn.table_exists('search_name'):
                 with conn.cursor() as cur:
                     cur.drop_table("word_frequencies")
                     LOG.info("Computing word frequencies")