Fix "page not found" handling in the router

[vbaranov]

Motivation

BS renders Page not found view if the path consists only from one part in URL (for instance /1). If the wrong path consists of multiple parts (for instance /1/2/3/4/5/6/), Blockscout doesn't handle them.

Changelog

Bug Fixes

• search mask for Page not found page changed to:
  https://github.com/poanetwork/blockscout/blob/7187e5766047df8fb0cf4840abb63f0b3616fa90/apps/block_scout_web/lib/block_scout_web/router.ex#L264

• Added missing function clauses for various controllers, that causes Internal server error when trying to open corresponding pages.

Checklist for your PR

• I added an entry to CHANGELOG.md with this PR
• If I added new functionality, I added tests covering it.
• If I fixed a bug, I added a regression test to prevent the bug from silently reappearing again.
• I checked whether I should update the docs and did so if necessary

[coveralls]

Pull Request Test Coverage Report for Build ec51249a-7e04-4a99-9f0f-94ba2c9b34e0

• 1 of 6 (16.67%) changed or added relevant lines in 5 files are covered.
• 70 unchanged lines in 6 files lost coverage.
• Overall coverage increased (+0.03%) to 79.551%

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Changes Missing Coverage	Covered Lines	Changed/Added Lines	%
apps/block_scout_web/lib/block_scout_web/controllers/address_logs_controller.ex	0	1	0.0%
apps/block_scout_web/lib/block_scout_web/controllers/chain_controller.ex	0	1	0.0%
apps/block_scout_web/lib/block_scout_web/controllers/smart_contract_controller.ex	0	1	0.0%
apps/block_scout_web/lib/block_scout_web/controllers/address_transaction_controller.ex	0	2	0.0%

Files with Coverage Reduction	New Missed Lines	%
apps/block_scout_web/lib/block_scout_web/controllers/chain_controller.ex	1	82.61%
apps/block_scout_web/lib/block_scout_web/controllers/api/v1/verified_smart_contract_controller.ex	1	61.11%
apps/block_scout_web/lib/block_scout_web/controllers/api/v1/decompiled_smart_contract_controller.ex	1	95.24%
apps/block_scout_web/lib/block_scout_web/controllers/api/rpc/block_controller.ex	2	75.0%
apps/block_scout_web/lib/block_scout_web/controllers/transaction_token_transfer_controller.ex	2	88.89%
apps/explorer/lib/explorer/chain.ex	63	81.06%

Totals
Change from base Build c6642e14-5998-4c1c-ab41-a5527de07294:	0.03%
Covered Lines:	5139
Relevant Lines:	6460

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💛 - Coveralls

[pasqu4le]

I only have a question