Fix probably cause of trie exception

[asdacap]

Fixes #4275

Fix TrieException due to pruning when a lower block produce sami storage root as newer block which causes it's LastSeen number to be reduced which will cause it to be memory pruned as no longer needed.

Changes:

• Ensure LastSeen does not get reduced

Types of changes

• Bugfix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Breaking change (fix or feature that would cause existing functionality to not work as expected)
• Documentation Update
• Code style update (formatting, renaming)
• Refactoring (no functional changes, no api changes)
• Build related changes
• Other (please describe):

Testing

Requires testing

• Yes
• No

In case you checked yes, did you write tests??

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• No

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