Syntax errors saved from `edit` could benefit from an error message

NB: one can put multiple statements into an `edit`. E.g. when editing a we can do:

5

b = 10

which will set a to 5 and b to 10

If the value of an `edit` in the editor has a syntax error, the remaining statements are not evaluated and there is no error message given.

E.g. when editing a:

'new_value'

b = illegal_syntax

a will take on its new value while b would stick with its old value despite no error message.

E.g. reversing the order for the syntax error when editing a:

illegal_syntax

b = 'new_value'

neither a nor b will take on new values, nor is there an error message.