🐛 Fix serve panics if splay is zero.

[preslavgerchev]

Running cnspec serve with the following config (relevant bits only included):

scan_interval:
  timer: 60

panics as the splay is 0. This PR adds a safeguard to ensure cnspec doesn't panic if it's only the timer that has been set

[github-actions]

Test Results

  1 files  ±0   24 suites  ±0   18s ⏱️ ±0s
322 tests ±0  321 ✅ ±0  1 💤 ±0  0 ❌ ±0 
323 runs  ±0  322 ✅ ±0  1 💤 ±0  0 ❌ ±0 

Results for commit 88a9c48. ± Comparison against base commit eba0d80.