Add guardclause of offset < 0 in #truncate

lib/gitlab/ci/trace/chunked_io.rb

@@ -134,7 +134,7 @@ module Gitlab
         end
 
         def truncate(offset)
-          raise ArgumentError, 'Outside of file' if offset > size
+          raise ArgumentError, 'Outside of file' if offset > size || offset < 0
           return if offset == size # Skip the following process as it doesn't affect anything
 
           @tell = offset