Fix comment line handling in sysusers.d(8) files

sysusers.d(8) format permits empty lines and commits, and so must we.
Add some extra fluff to the test-case for this.

This is the second half of
https://bugzilla.redhat.com/show_bug.cgi?id=2246236

Fixes: #2741

fileattrs/sysusers.attr

@@ -6,6 +6,9 @@
 # For groups created as a side-effect, only provide the group.
 %__sysusers_provides() %{lua:
     for line in io.lines(macros["1"]) do
+        if line:sub(1, 1) == '#' then
+            goto continue
+        end
         fields = {}
         for w in line:gmatch("%S+") do
             table.insert(fields, w)
@@ -14,5 +17,6 @@
             table.insert(fields, 1, '-b')
             print(macros.add_sysuser(fields))
         end
+        ::continue::
     end
 }

tests/data/SPECS/klang.spec

@@ -45,7 +45,12 @@ cat << EOF > ${RPM_BUILD_ROOT}/%{_sysusersdir}/klangd.conf
 u klangd - "Klang server" /var/lib/klangd /sbin/nologin
 EOF
 cat << EOF > ${RPM_BUILD_ROOT}/%{_sysusersdir}/plong.conf
+
+# Real life files have all sorts of anomalies
 u plong - "Plong fu" /var/lib/plong /sbin/nologin
+#...such as empty lines
+
+# and comments comments
 g klong -
 m ding dong
 r - 123-321