Add error handling if legaldoc file not found

Closes #1452

app/controllers/admin/legal_documents_controller.rb

@@ -5,7 +5,14 @@ module Admin
     def show
       @ld = LegalDocument.find(params[:id])
       filename = @ld.path.split('/').last
-      send_data File.open(@ld.path).read, filename: filename
+      file = File.open(@ld.path).read
+
+      if file
+        send_data file, filename: filename
+      else
+        flash[:notice] = I18n.t('legal_doc_not_found')
+        redirect_to [:admin, @ld.documentable]
+      end
     end
   end
 end

config/locales/admin/legal_documents.en.yml

@@ -0,0 +1,2 @@
+en:
+  legal_doc_not_found: "There is an error downloading legal document: file not found"

config/locales/admin/legal_documents.et.yml

@@ -0,0 +1,2 @@
+et:
+  legal_doc_not_found: "Viga juriidilise dokumendi allalaadimisel: faili ei leitud"