Add better error handling, correct the location on disk of stylesheet

app/controllers/stylesheets_controller.rb

@@ -8,7 +8,7 @@ class StylesheetsController < ApplicationController
     digest = "_" + digest if digest
 
     # Security note, safe due to route constraint
-    location = "#{DiscourseStylesheets::CACHE_PATH}/#{target}#{digest}.css"
+    location = "#{Rails.root}/#{DiscourseStylesheets::CACHE_PATH}/#{target}#{digest}.css"
 
     unless File.exist?(location)
       query = StylesheetCache.where(target: target)

app/models/stylesheet_cache.rb

@@ -20,6 +20,8 @@ class StylesheetCache < ActiveRecord::Base
     success
   rescue ActiveRecord::RecordNotUnique
     false
+  rescue PG::UniqueViolation
+    false
   end
 
 end

lib/sass/discourse_stylesheets.rb

@@ -89,7 +89,11 @@ class DiscourseStylesheets
     File.open(stylesheet_fullpath, "w") do |f|
       f.puts css
     end
-    StylesheetCache.add(@target, digest, css)
+    begin
+      StylesheetCache.add(@target, digest, css)
+    rescue => e
+      Rails.logger.warn "Completely unexpected error adding item to cache #{e}"
+    end
     css
   end