Making error message more user-friendly with spaces in a URI

Hi,

I made a patch to make the error message more user-friendly when using a
URI to connect a database with psql.

Current Error Message:

$ psql "postgres://localhost:5432/postgres?application_name=a b"
psql: error: trailing data found: "a b"

Currently, if spaces exist in the URI, psql displays this generic error
message.

New Error Message (with patch):

psql: error: found unexpected spaces: “a b“. Did you forget to
percent-encode spaces?

This revised message is clearer and more concise, guiding users to check
for encoding issues.

Regards,
Yushi Ogiwara