case 1 is already handled in the first lines of the for loop;
it would only be entered in the invalid case where the string
continues past the defined length (ch != 0 but length-- == 0).

case 2 and case 3 are redundant, since k >= j and later the
string is truncated to j characters anyway.

This added check is actually for NOT failing in NON-strict mode.
The ch == -2 check later causes the desired failure in strict mode.

If length == 0 || *current != '=' is false, the for loop will always
end up in this same point, until the if statement becomes true.
Thus, the if statement is not needed.