Refactor `filter_valid_projects` utility function to handle edge cases

[andersy005]

this pr fixes a bug in filter_valid_projects function to ensure

• /charts/credits_by_transaction_date?transaction_type=issuance and
• /charts/credits_by_transaction_date?transaction_type=issuance&registry=verra&registry=gold-standard&registry=global-carbon-council&registry=american-carbon-registry&registry=climate-action-reserve&registry=art-trees&category=agriculture&category=biochar&category=cookstoves&category=energy-efficiency&category=forest&category=grassland&category=industrial-gases&category=industrial-processes&category=land-use&category=landfill&category=livestock&category=mine-methane&category=oil-and-gas&category=renewable-energy&category=soil&category=transportation&category=unknown&category=waste-management

queries to return the same thing

before

• https://offsets-db-staging.fly.dev/charts/credits_by_transaction_date?transaction_type=issuance&registry=verra&registry=gold-standard&registry=global-carbon-council&registry=american-carbon-registry&registry=climate-action-reserve&registry=art-trees&category=agriculture&category=biochar&category=cookstoves&category=energy-efficiency&category=forest&category=grassland&category=industrial-gases&category=industrial-processes&category=land-use&category=landfill&category=livestock&category=mine-methane&category=oil-and-gas&category=renewable-energy&category=soil&category=transportation&category=unknown&category=waste-management

{
  "pagination": {
    "total_entries": 10,
    "current_page": 1,
    "total_pages": 1,
    "next_page": null
  },

• https://offsets-db-staging.fly.dev/charts/credits_by_transaction_date?transaction_type=issuance

{
  "pagination": {
    "total_entries": 20,
    "current_page": 1,
    "total_pages": 1,
    "next_page": null
  },

after

• https://offsets-db-staging.fly.dev/charts/credits_by_transaction_date?transaction_type=issuance&registry=verra&registry=gold-standard&registry=global-carbon-council&registry=american-carbon-registry&registry=climate-action-reserve&registry=art-trees&category=agriculture&category=biochar&category=cookstoves&category=energy-efficiency&category=forest&category=grassland&category=industrial-gases&category=industrial-processes&category=land-use&category=landfill&category=livestock&category=mine-methane&category=oil-and-gas&category=renewable-energy&category=soil&category=transportation&category=unknown&category=waste-management

{
  "pagination": {
    "total_entries": 20,
    "current_page": 1,
    "total_pages": 1,
    "next_page": null
  },

• https://offsets-db-staging.fly.dev/charts/credits_by_transaction_date?transaction_type=issuance

{
  "pagination": {
    "total_entries": 20,
    "current_page": 1,
    "total_pages": 1,
    "next_page": null
  },

cc @katamartin