Ignore input with whitespace only

[asdine]

Whenever we press return with no input or whitespace only input in the CLI, it invites the user to add a ;.
We should simply ignore the input.

Current behavior:

genji> <press return, with or without whitespace>
... <press ';', then return>
genji>

Expected behavior:

genji> <press return, with or without whitespace>
genji>

[yaziine]

If we run a query with whitespace after the ;, it also invites to add a ;.

genji> create table foo; <press return with whitespace after the ; >
... <press ';', then return>
genji>