优化修改Air530Z_GetPos2D()函数，加强健壮性，解决程序退出时，串口释放后的偶发性崩溃

air530z/air530z.c

@@ -181,6 +181,7 @@ int Air530Z_ComExit()
 int Air530Z_GetPos2D(char lat[MAX_LINE_CHARS], char lon[MAX_LINE_CHARS])
 {
   bool bOK = false;
+  if(!s_myCom.h || !s_myCom.out_rwlock) return -1; // 防御检查, 加强健壮性
   sw_rwlock_rdlock(s_myCom.out_rwlock, WAIT_FOREVER);
   bOK = s_myCom.outPos2d.bOK;
   if(bOK) {