Modules Stop Being Added if A Single One Can't Be Found

If you have a string of modules being enabled with "drush dslm-add-contrib" and the third module isn't found, the first two will be enabled but the fourth one won't be be enabled. This can cause issues if the added modules depend on each other and errors arise when one module isn't present.

A proposed solution would be to check to see if all modules are listed in a package, and if one isn't found, ask the user if they want to continue trying to add and enable all of the modules.