Inverted conditionals in estimates and invoices lists to use 'unless'

app/views/estimates/_list.html.erb

@@ -1,4 +1,4 @@
-<% if estimates.empty? %>
+<% unless estimates.empty? %>
 
   <% estimates.sort.reverse.each do |estimate| %>
     <div class="row">

app/views/invoices/_list.html.erb

@@ -1,4 +1,4 @@
-<% if invoices.empty? %>
+<% unless invoices.empty? %>
 
   <%= form_with(url: invoice_path, method: :get) do |form| %>