Fix missing error handling for 'sqlite3_step' on 'SQLite3_result'

Error handling for 'sqlite3_step' should be performed in a similar
fashion as for 'sqlite3_exec'. Not handling these potential errors could
result in invalid empty/incomplete resultsets when reading from the
internal SQLite3 databases.

lib/sqlite3db.cpp

@@ -764,7 +764,13 @@ void SQLite3_result::add_column_definition(int a, const char *b) {
  * @return An integer representing the result of the operation (SQLITE_ROW on success).
  */
 int SQLite3_result::add_row(sqlite3_stmt *stmt, bool skip) {
-	int rc=(*proxy_sqlite3_step)(stmt);
+	int rc = 0;
+	do {
+		rc = (*proxy_sqlite3_step)(stmt);
+		if (rc == SQLITE_BUSY || rc == SQLITE_LOCKED) {
+			usleep(USLEEP_SQLITE_LOCKED);
+		}
+	} while (rc == SQLITE_BUSY || rc == SQLITE_LOCKED);
 	if (rc!=SQLITE_ROW) return rc;
 	if (skip==false) {
 		SQLite3_row *row=new SQLite3_row(columns);