The Item_func_if::fix_length_and_dec() function when calculating length of 
result doesn't take into account unsigned_flag. But it is taken when 
calculating length of temporary field. This result in creating field that 
shorter than needed. Due to this, in the reported query 40.0 converted to 9.99.

The function Item_func_if::fix_length_and_dec() now adds 1 to the max_length if 
the unsigned_flag isn't set.


sql/item_cmpfunc.cc:
  Fixed bug#16272: IF function with decimal args can produce wrong result
  The function Item_func_if::fix_length_and_dec() now adds 1 to the max_length if 
  the unsigned_flag isn't set.
mysql-test/r/func_if.result:
  Added test case for bug#16272: IF function with decimal args can produce wrong result
mysql-test/t/func_if.test:
  Added test case for bug#16272: IF function with decimal args can produce wrong result