[core] Fix subtle bug in OfflineDatabase with updated resources

SQLite REPLACE is *not* UPSERT. If a conflict occurs, it first deletes the existing row, then inserts a new row. This means that AUTOINCREMENT primary keys change. This will break foreign keys to that value, which we use.

Instead we must try an UPDATE, and fall back to an INSERT if the UPDATE changes zero rows.

platform/default/sqlite3.cpp

@@ -292,6 +292,24 @@ template <> std::chrono::system_clock::time_point Statement::get(int offset) {
     return std::chrono::system_clock::from_time_t(sqlite3_column_int64(stmt, offset));
 }
 
+template <> optional<int64_t> Statement::get(int offset) {
+    assert(stmt);
+    if (sqlite3_column_type(stmt, offset) == SQLITE_NULL) {
+        return optional<int64_t>();
+    } else {
+        return get<int64_t>(offset);
+    }
+}
+
+template <> optional<double> Statement::get(int offset) {
+    assert(stmt);
+    if (sqlite3_column_type(stmt, offset) == SQLITE_NULL) {
+        return optional<double>();
+    } else {
+        return get<double>(offset);
+    }
+}
+
 template <> optional<std::string> Statement::get(int offset) {
     assert(stmt);
     if (sqlite3_column_type(stmt, offset) == SQLITE_NULL) {