when a divisor is less than 1 and its fractional part is very long.
For example:
1 % .123456789123456789123456789123456789123456789123456789123456789123456789123456789;

Stack buffer overflow has been fixed in the do_div_mod function.


strings/decimal.c:
  Fixed bug #31019.
  Stack buffer overflow has been fixed in the do_div_mod function:
  a value of the upper bound of the buffer was increased where
  a decrement is required.
mysql-test/t/type_decimal.test:
  Added test case for bug #31019.
mysql-test/r/type_decimal.result:
  Added test case for bug #31019.