Ignore binary files in code search to prevent Error 500

Leaving out the -I option in "git grep" would cause an Error 500 because the
resulting line would include "Binary file X matches"

CHANGELOG

@@ -2,6 +2,7 @@ Please view this file on the master branch, on stable branches it's out of date.
 v 8.5.0 (unreleased)
   - Add "visibility" flag to GET /projects api endpoint
+  - Ignore binary files in code search to prevent Error 500 (Stan Hu)
   - Upgrade gitlab_git to 7.2.23 to fix commit message mentions in first branch push
   - New UI for pagination

app/models/repository.rb

@@ -598,7 +598,7 @@ class Repository
   def search_files(query, ref)
     offset = 2
-    args = %W(#{Gitlab.config.git.bin_path} grep -i -n --before-context #{offset} --after-context #{offset} -e #{query} #{ref || root_ref})
+    args = %W(#{Gitlab.config.git.bin_path} grep -i -I -n --before-context #{offset} --after-context #{offset} -e #{query} #{ref || root_ref})
     Gitlab::Popen.popen(args, path_to_repo).first.scrub.split(/^--$/)
   end