FAST orderbook: set glasks and glbids to NULL explicitly
FAST orderbook: set glasks and glbids to NULL explicitly

Once a particular order book is finalized (ob_fini() is called)
we must not refer to internal structures anymore as they are
released. Hence ob_init() is to make sure that internal structures
are initialized before a user is allowed to refer to them.

Otherwise we are exposed to illegal memory access:

ob_fini();
ob_init();

refer to glasks/glbids will lead to SIGSEGV

Signed-off-by: Marat Stanichenko <146c4a279a7427b2cc19a19b6130cbb7ee404ab1@gmail.com>

Bitcoinsulting/libtrading,mstanichenko/libtrading,fengzhyuan/libtrading,jvirtanen/libtrading,Bitcoinsulting/libtrading,femtotrader/libtrading,etoestja/libtrading,svdev/libtrading,fengzhyuan/libtrading,penberg/libtrading,divaykin/libtrading,svdev/libtrading,penberg/libtrading,etoestja/libtrading,NunoEdgarGub1/libtrading,jvirtanen/libtrading,NunoEdgarGub1/libtrading,libtrading/libtrading,mstanichenko/libtrading,libtrading/libtrading,divaykin/libtrading,femtotrader/libtrading