fix infinite loop of setting state then useEffect in ItemViewer

[nbarlowATI]

Slightly hacky (but very minimal) fix: to avoid calling setItems inside useEffect (which leads to an infinite loop, as setting the state triggers a re-render, which calls useEffect) - just check if the item has changed.
Closes #69

[coveralls]

Pull Request Test Coverage Report for Build 2089405586

• 0 of 0 changed or added relevant lines in 0 files are covered.
• No unchanged relevant lines lost coverage.
• Overall coverage increased (+0.1%) to 90.674%

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Totals
Change from base Build 2089390822:	0.1%
Covered Lines:	982
Relevant Lines:	1083

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💛 - Coveralls

[coveralls]

Pull Request Test Coverage Report for Build 2089731232

• 0 of 0 changed or added relevant lines in 0 files are covered.
• No unchanged relevant lines lost coverage.
• Overall coverage increased (+0.1%) to 90.674%

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Totals
Change from base Build 2089390822:	0.1%
Covered Lines:	982
Relevant Lines:	1083

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💛 - Coveralls

[mhauru]

Nice!