EXT-8259 FIXED Fixed occasional truncation of the "More" link in expandable textboxes.

The bug seems to happen when the text contains trailing newlines.
So the workaround is to strip those newlines.
I use a workaround because a proper fix might require changing LLTextBase which is undesirable at this point.

Reviewed by Mike Antipov at https://codereview.productengine.com/secondlife/r/722/

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branch : product-engine