Attribute transformers generate unnecessary IDs

[schlessera]

The transformers in ApplyCommonAttributes.js generate unnecessary IDs in the following cases:

• sizes attribute present but srcset not set: 410be25#diff-cf10c25ff7f458a7c839e092accc68cfR12
• media attribute present but empty: 410be25#diff-f2a4be815edc144ecbc86a09e3fc0f9cR12

In these instances, no CSS is added (you can see that the first ID used within the CSS is 1, not 0), so the HTML markup should not be made longer by adding an unused ID.