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.

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

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.