Fix potential out of bounds index in test

Author: Juuso Mäyränen

spec/inputs/redis_spec.rb

@@ -26,12 +26,14 @@ def wait_events(conf, event_count)
 end
 
 def process(conf, event_count)
+  expect(event_count).to be > 0
   events = wait_events(conf, event_count)
   # due multiple workers we get events out-of-order in the output
   events.sort! { |a, b| a.get('sequence') <=> b.get('sequence') }
-  expect(events[0].get('sequence')).to eq(0)
-  expect(events[100].get('sequence')).to eq(100)
-  expect(events[1000].get('sequence')).to eq(1000)
+  [0, 100, 1000].each do |idx|
+    idx = [idx, event_count - 1].min
+    expect(events[idx].get('sequence')).to eq idx
+  end
 end
 
 # integration tests ---------------------