temp env vs export

[Grisha Levit]

Using `export' / `readonly' on a variable that's present in both the temp
env and a calling function's local context combines the attributes of all
the intervening scopes in the global variable:

$ declare -A v; f() { local -a v; v= e; }; e() { export v; }
$ (f; declare -p v)
declare -aAx v=([0]="")
$ (f; v=)
Segmentation fault: 11