Don't attempt to include too large diffs in e-mail-on-push messages

Possible cause of issues in gitlab-org/gitlab-ce#15137

CHANGELOG-EE

 Please view this file on the master branch, on stable branches it's out of date.
 
 v 8.7.0 (unreleased)
+  - Don't attempt to include too large diffs in e-mail-on-push messages (Stan Hu)
   - Update GitLab Pages to 0.2.1: support user-defined 404 pages
   - Refactor group sync to pull access level logic to its own class. !306
   - [Elastic] Stabilize database indexer if database is inconsistent

app/views/notify/repository_push_email.html.haml

@@ -48,6 +48,9 @@
   - unless @message.disable_diffs?
     - diff_files = @message.diffs
 
+    - if @message.compare_timeout
+      %h5 The diff was not included because it is too large.
+    - else
       %h4 Changes:
       - diff_files.each_with_index do |diff_file, i|
         %li{id: "diff-#{i}"}
@@ -76,5 +79,3 @@
             No preview for this file type
           %br
 
-  - if @message.compare_timeout
-    %h5 Huge diff. To prevent performance issues changes are hidden

app/views/notify/repository_push_email.text.haml

@@ -25,6 +25,11 @@
     - else
       \- #{diff.new_path}
   - unless @message.disable_diffs?
+    - if @message.compare_timeout
+      \
+      \
+      The diff was not included because it is too large.
+    - else
       \
       \
       Changes:
@@ -39,10 +44,7 @@
           = diff_file.new_path
         \=====================================
         != diff_file.diff.diff
-  - if @message.compare_timeout
-    \
-    \
-    Huge diff. To prevent performance issues it was hidden
+
   - if @message.target_url
     \
     \