google auth uri spec query re: falsy strings

The code for generating the qrcode message makes quick checks to see if a string is "falsy", presumably intending to check if it's empty.

This means that a `$label` or `$issuer` of `''` is treated identically to `'0'` and `' '`.

How is trailing whitespace meant to be handled in these uris- i.e. should it be simply checking `'' !== $label`, or trim them first?