fix the build_changes_sql query to include cases where col_value is null (for example when col_name = CLOUDSYNC_TOMBSTONE_VALUE)

Author: andinux

src/vtab.c

@@ -148,7 +148,8 @@ char *build_changes_sql (sqlite3 *db, const char *idxs) {
     "        COALESCE(t2.col_version, 1) AS cl "
     "     FROM \"' || \"table_meta\" || '\" AS t1 "
     "     LEFT JOIN cloudsync_site_id AS site_tbl ON t1.site_id = site_tbl.rowid "
-    "     LEFT JOIN \"' || \"table_meta\" || '\" AS t2 ON t1.pk = t2.pk AND t2.col_name = ''" CLOUDSYNC_TOMBSTONE_VALUE "'' WHERE col_value != ''" CLOUDSYNC_RLS_RESTRICTED_VALUE "''' "
+    "     LEFT JOIN \"' || \"table_meta\" || '\" AS t2 ON t1.pk = t2.pk AND t2.col_name = ''" CLOUDSYNC_TOMBSTONE_VALUE "'' "
+    "     WHERE col_value IS NOT ''" CLOUDSYNC_RLS_RESTRICTED_VALUE "''' "
     "    AS query_string FROM table_names "
     "), "
     "union_query AS ( "