Trailing new-line character incorrectly triggers a request to /import

[tnajdek]

Pasting a single line with a trailing new-line character should not trigger metadata parsing (#260). For example pasting

978-0006479888

(including the trailing new line) into zbib does not work but then pressing "Cite" works.

This might be the cause for https://forums.zotero.org/discussion/108957/zbib-error-on-ipads-using-isbn - I wasn't able to reproduce the exact problem but noticed that when text is copied on iOS it's more likely it contains a trailing \n even though selected source doesn't visually extend to the new line and the same text selected and copied on desktop does not.