Fix number comparison in number_to_amount() in number_helper.php

[sba]

Description
replaces #7648

1000 gives 1 thousand and not 1000
1000000 gives 1 million and not 1000 thousand
and so on...

And it compares now the same way like the function number_to_size above

Checklist:

• Securely signed commits
• Component(s) with PHPDoc blocks, only if necessary or adds value
• Unit testing, with >80% coverage
• User guide updated
• Conforms to style guide

[kenjis]

Thank you.