org settings: Return `undefined` in get_input_element_value.
org settings: Return `undefined` in get_input_element_value.

This change makes `.get_input_element_value()` return a `undefined` instead
of `null` when `input_type` is not defined. Which also make sense
logically, as

> null: absence of value for a variable;

> undefined: absence of variable itself;

Source: https://stackoverflow.com/q/5076944/7418550

andersk/zulip,hackerkid/zulip,timabbott/zulip,shubhamdhama/zulip,hackerkid/zulip,punchagan/zulip,synicalsyntax/zulip,eeshangarg/zulip,kou/zulip,kou/zulip,kou/zulip,punchagan/zulip,brainwane/zulip,hackerkid/zulip,brainwane/zulip,eeshangarg/zulip,timabbott/zulip,synicalsyntax/zulip,brainwane/zulip,rht/zulip,rht/zulip,timabbott/zulip,hackerkid/zulip,punchagan/zulip,kou/zulip,rht/zulip,brainwane/zulip,timabbott/zulip,timabbott/zulip,synicalsyntax/zulip,hackerkid/zulip,showell/zulip,zulip/zulip,zulip/zulip,showell/zulip,shubhamdhama/zulip,eeshangarg/zulip,timabbott/zulip,andersk/zulip,rht/zulip,shubhamdhama/zulip,shubhamdhama/zulip,kou/zulip,showell/zulip,showell/zulip,rht/zulip,shubhamdhama/zulip,timabbott/zulip,zulip/zulip,punchagan/zulip,shubhamdhama/zulip,punchagan/zulip,brainwane/zulip,andersk/zulip,brainwane/zulip,eeshangarg/zulip,hackerkid/zulip,synicalsyntax/zulip,hackerkid/zulip,punchagan/zulip,showell/zulip,andersk/zulip,showell/zulip,zulip/zulip,andersk/zulip,rht/zulip,rht/zulip,kou/zulip,zulip/zulip,eeshangarg/zulip,zulip/zulip,shubhamdhama/zulip,zulip/zulip,punchagan/zulip,synicalsyntax/zulip,synicalsyntax/zulip,andersk/zulip,andersk/zulip,eeshangarg/zulip,kou/zulip,brainwane/zulip,showell/zulip,synicalsyntax/zulip,eeshangarg/zulip