fix(functions): Ensure functions timeseries is non empty (#53462)

It's possible that the timeseries is an empty array which will error
when we try to use the first 20% as historical data. Make sure to handle
this.

Fixes SENTRY-1402

src/sentry/api/endpoints/organization_profiling_functions.py

@@ -178,6 +178,7 @@ def get_trends_data(stats_data):
  "request_end": v[data["function"]]["end"],
  }
  for k, v in stats_data.items()
+ if v[data["function"]]["data"]
  },
  "sort": data["trend"].as_sort(),
  "trendFunction": data["function"],