Use disabledText only when multiselect is actually disabled

[adeeb1]

Builds on https://github.com/davidstutz/bootstrap-multiselect/pull/715 to fix https://github.com/davidstutz/bootstrap-multiselect/issues/714.

Previously, the disabledText will display if no options are selected on the multiselect and disableIfEmpty is set to true, even if there are options present in the multiselect. I changed the condition to check for the number of total options in the select rather than the number of selected options. Whether or not any options are selected is irrelevant.