help to prevent current data in file from causing TDengine crashed while min/max function is invoked.

fix the bug in #1094. [tbase-1450]

fix bug that failed to add the number of blocks in the records (SMeterDataInfo) for each table

increase the value range for pSql->numOfSubs from uint8_t to uint16_t

prepare all subqueries object before launch subqueries. and add some check for global status object  during super table query.

add the union support in sql parser: fix memory leaks and refactor some functions, improve the performance of some functions. #1032. [TBASE-1140]

fix the invalid release operations when the database is dropped and the metermeta cache is cleaned up at the client side. #1053  [tbase-1435]