ASSERT happens due to improper calculation of the max_length
in Item_func_div object, if dividend has max_length == 0 then
Item_func_div::max_length is set to 0 under some circumstances.
The fix:
If decimals == NOT_FIXED_DEC then set
Item_func_div::max_length to max possible
DOUBLE length value.


mysql-test/r/func_math.result:
  test case
mysql-test/t/func_math.test:
  test case
sql/item_func.cc:
  The fix:
  If decimals == NOT_FIXED_DEC then set
  Item_func_div::max_length to max possible
  DOUBLE length value.