preserve trailing word boundaries

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this PR resolves the bug described in #1544

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this issue appears to be more complex than I had hoped, it would take some more time to investigate:

• whether clean.text is producing the correct value
• whether _sanitizer/_tokinizer.js is marking all tokens as 'complete' when the text has extra chars at the end
• whether the parser is receiving what it needs and returning the correct thing
• what effect (if any) changes would have on /v1/search

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note: there is already some code which is fairly similar looking but subtly different from the changes in this PR:

api/sanitizer/_tokenizer.js

Lines 41 to 45 in e6179c5

	// when $subject is not the end of $clean.text
	// then there must be tokens coming afterwards
	else if (!clean.text.endsWith(text)) {
	parserConsumedAllTokens = true;
	}