Don't seek at all if the log is small anyway

then it's fine to skip the first line because
it won't be very noticeable

lib/gitlab/ci/trace/stream.rb

@@ -25,13 +25,11 @@ module Gitlab
         end
 
         def limit(last_bytes = LIMIT_SIZE)
-          stream_size = size
-          if stream_size < last_bytes
-            last_bytes = stream_size
-          end
+          if last_bytes < size
             stream.seek(-last_bytes, IO::SEEK_END)
             stream.readline
           end
+        end
 
         def append(data, offset)
           stream.truncate(offset)