FIX: statistics_host returns if no host value is given

[waldbauer-certat]

Fixes #2103

[codecov-commenter]

Codecov Report

Merging #2104 (aaf90df) into develop (9f07fcb) will decrease coverage by 0.04%.
The diff coverage is 42.19%.

@@             Coverage Diff             @@
##           develop    #2104      +/-   ##
===========================================
- Coverage    76.07%   76.03%   -0.05%     
===========================================
  Files          429      434       +5     
  Lines        23070    23221     +151     
  Branches      3085     3105      +20     
===========================================
+ Hits         17551    17656     +105     
- Misses        4812     4854      +42     
- Partials       707      711       +4     

Impacted Files	Coverage Δ
intelmq/bots/collectors/http/collector_http.py	59.61% <ø> (ø)
...elmq/bots/collectors/http/collector_http_stream.py	40.00% <ø> (ø)
intelmq/bots/collectors/misp/collector.py	41.86% <ø> (ø)
...s/collectors/shadowserver/collector_reports_api.py	89.28% <ø> (ø)
intelmq/bots/outputs/misp/output_api.py	24.75% <ø> (ø)
intelmq/bots/parsers/hibp/parser_callback.py	94.44% <ø> (ø)
intelmq/bots/parsers/microsoft/parser_ctip.py	85.88% <ø> (ø)
intelmq/bots/parsers/shadowserver/_config.py	98.73% <ø> (ø)
intelmq/bots/parsers/shadowserver/parser_json.py	78.50% <ø> (ø)
intelmq/lib/bot_debugger.py	20.52% <0.00%> (ø)
... and 103 more

[ghost]

That is only applicable because the only code calling this cache is the bots.py for the statistics. If any other code would use this class, this fix silently ignores misconfiguration

[ghost]

please add a changelog entry