[PATCH] Do not set default terms if no default terms are configured

If for whatever reason you are setting certain terms programaticaly on your own module, and you have this module installed, taxonomy_defaults will take over the vocabulary and your code will stop working.

This is because the module doesn't check wether or not there are any default terms selected for that content type & vocab when setting its defaults in form_alter.

The attached patch fixes this issue. It should also improve a bit performance of the node forms since it stops the flow if no default terms are set.