Fixed MDEV-5724 "Server crashes on SQL select containing more group by and left join statements using innodb tables"
  
The problem was that a big record was allocated on the stack, which casued stack to run out.
  
Fixed by using my_safe_alloca() instead of my_alloca() when allocating records.
Now only records <= 16384 are allocated on the stack.

mysql-test/r/stack-crash.result:
  Added test case
mysql-test/t/stack-crash.test:
  Added test case
storage/maria/ma_blockrec.c:
  Use my_safe_alloca() instead of my_alloca()
storage/maria/ma_dynrec.c:
  Use my_safe_alloca() instead of my_alloca()
storage/maria/maria_def.h:
  Added MARIA_MAX_RECORD_ON_STACK
storage/maria/maria_pack.c:
  Use my_safe_alloca() instead of my_alloca()