State of admin menu boxes not remembered since r16813

[demetris]

Starting with r16813, the collapsed/expanded state of admin menu boxes is not remembered.

[nacin]

Worse things have happened :-)

It appears to be inconsistent. Perhaps a page behind?

[demetris]

@nacin: It seems to remember the state the boxes were in before r16813, but does not remember any changes you make.

[ocean90]

id is an empty string, so the if ( id ) {...} condition fails.

[nacin]

(In [16874]) Fix admin menu save state. props greuben, fixes #15767, see #15615.