awful.tag.new: Handle too few given layouts

When awful.tag.new() got a list of layouts shorter than the list of
names, it would previously create tags with nil as their layout. This
commit changes this so that the first layout is repeated if necessary.

Related-to: https://github.com/awesomeWM/awesome/issues/1853
Signed-off-by: Uli Schlachter <psychon@znc.in>

lib/awful/tag.lua

@@ -240,11 +240,15 @@ end
 -- @return A table with all created tags.
 function tag.new(names, screen, layout)
     screen = get_screen(screen or 1)
+    -- True if `layout` should be used as the layout of each created tag
+    local have_single_layout = (not layout) or (layout.arrange and layout.name)
     local tags = {}
     for id, name in ipairs(names) do
-        table.insert(tags, id, tag.add(name, {screen = screen,
-                                            layout = (layout and layout[id]) or
-                                                        layout}))
+        local l = layout
+        if not have_single_layout then
+            l = layout[id] or layout[1]
+        end
+        table.insert(tags, id, tag.add(name, {screen = screen, layout = l}))
         -- Select the first tag.
         if id == 1 then
             tags[id].selected = true