lib: fix invalid error for uri_content

It is not possible to universally call :path() on URIs as not all of
them are of file scheme. Instead :uri() should have been called here to
get URI representation.

This also not essentially downloading URI. It just receives it no matter
what kind of URI it is so message about download is miss leading
(although in most cases valid).
7 jobs for fix-invalid-error in 4 minutes and 57 seconds (queued for 7 seconds)
Status Job ID Name Coverage
  Build
passed #378167
build-alpine

00:01:13

passed #378165
build-debian-stable

00:01:10

passed #378166
build-debian-unstable

00:01:09

 
  Test
passed #378168
check

00:01:51

passed #378170
lint-c

00:00:47

passed #378171
lint-lua

00:00:48

passed #378169
valgrind-memcheck

00:03:43