Current code was relying on grade_floatval() that is not a validation
function. Instead, the gradepass field must be defined as proper float
and then perform the needed validations using unformat_float().
Note that the float element form has some particularities, see
MDL-73994 for more information and that makes us to have to check
for some values (null, zero) manually. Once that form element type
gets its behaviour fixed, the code will need to be revisited, hence
we have annotated it as comments for easier finding it in the future
(the same changes already were applied to other gradebook forms).
Also, remove an unreachable line of code (comparing with empty string)
within the grade_floatval() function because it's not possible anymore
to pass any string to it, as far as it's "?float" typed.
Covered as many cases with quiz completion as have been able to imagine.
b3b1006201