PVS-Studio warning V595 for Firebird

int CCH_down_grade_dbb(void* ast_object)
{
  ....
  SyncLockGuard bcbSync(&bcb->bcb_syncObject, SYNC_EXCLUSIVE,
                        "CCH_down_grade_dbb");
  bcb->bcb_flags &= ~BCB_exclusive;

  if (bcb && bcb->bcb_count)
  ....
}

This suspicious code was found in Firebird project by PVS-Studio static code analyzer.
Warning message is:
V595 The 'bcb' pointer was utilized before it was verified against nullptr. Check lines: 271, 274. cch.cpp 271

PVS-Studio is a static analyzer for detecting bugs in the source code of applications written in C, C++, C++11, C++/CX. Site: http://www.viva64.com/en/pvs-studio/