apply back button trim only if length >= 7

pull-request #512 for `2.1devtf` branch

Issue
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if backButton text is 5 characters then "..." is added, for example if text is "Title" becomes "Title..."

Test Case
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Make the title of a page to 5 character title, and navigate to a different page, notice that the bacButton has 5 characters + "..."

Fix
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add another check to append "..." only `if (text.length >= 7)` this will make sure that "..." is only appended if text is 7 characters or more, and truncates at 5 characters.