Fix adding state events to the database

[S7evinK]

When we're adding state to the database, we check which eventNIDs are already in a block, if we already have that eventNID, we remove it from the list. In its current form we would skip over eventNIDs in the case we already found a match (we're decrementing i twice)
My theory is, that when we later get the state blocks, we are receiving "too many" eventNIDs (well, yea, we stored too many), which may or may not can result in state resets when comparing different state snapshots. (e.g. when adding state we stored a eventNID by accident because we skipped it, later we add more state and are not adding it because we don't skip it)

[codecov]

Codecov Report

Patch coverage: 50.00% and project coverage change: -0.05 ⚠️

Comparison is base (2ee03fd) 65.56% compared to head (b1add4c) 65.51%.

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #3133      +/-   ##
==========================================
- Coverage   65.56%   65.51%   -0.05%     
==========================================
  Files         504      504              
  Lines       56055    56055              
==========================================
- Hits        36751    36727      -24     
- Misses      15517    15531      +14     
- Partials     3787     3797      +10     

Flag	Coverage Δ
unittests	49.79% <50.00%> (-0.07%)	⬇️

Flags with carried forward coverage won't be shown. Click here to find out more.

Impacted Files	Coverage Δ
roomserver/storage/shared/storage.go	67.02% <50.00%> (-0.39%)	⬇️

... and 14 files with indirect coverage changes

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