Revert to previous diff pruning behavior

Before 10.6.9, if a rugged diff met the conditions for being too-large
(which obiously meant it was also collapsable), too-large would take
precedence. This reverts the behavior back to that, since gitlab-ce
depends on this

CHANGELOG

 v 10.6.10
   - Ignore invalid encodings when parsing Git attribute files
+  - Revert to previous diff pruning behavior
 v 10.6.9
   - Optimize diff creation from Rugged::Patch

lib/gitlab_git/diff.rb

@@ -290,14 +290,14 @@ module Gitlab
               prune_large_diff!
               return true
             end
-
-            if collapse && size >= DIFF_COLLAPSE_LIMIT
-              prune_collapsed_diff!
-              return true
-            end
           end
         end
+        if collapse && size >= DIFF_COLLAPSE_LIMIT
+          prune_collapsed_diff!
+          return true
+        end
+
         false
       end

spec/diff_spec.rb

@@ -80,6 +80,24 @@ EOT
         end
       end
+      context 'using a collapsable diff that is too large' do
+        before do
+          # The patch total size is 200, with lines between 21 and 54.
+          # This is a quick-and-dirty way to test this. Ideally, a new patch is
+          # added to the test repo with a size that falls between the real limits.
+          stub_const('Gitlab::Git::Diff::DIFF_SIZE_LIMIT', 150)
+          stub_const('Gitlab::Git::Diff::DIFF_COLLAPSE_LIMIT', 100)
+        end
+
+        it 'prunes the diff as a large diff instead of as a collapsed diff' do
+          diff = Gitlab::Git::Diff.new(@rugged_diff, collapse: true)
+
+          expect(diff.diff).to be_empty
+          expect(diff).to be_too_large
+          expect(diff).not_to be_collapsed
+        end
+      end
+
       context 'using a large binary diff' do
         it 'does not prune the diff' do
           expect_any_instance_of(Rugged::Diff::Delta).to receive(:binary?).