resolve crashes with ICU 53.1 in locales with collator data, fdo#77071

ICU 53.1 changed API behavior:
https://ssl.icu-project.org/apiref/icu4c/classicu_1_1RuleBasedCollator.html#a2f4c7eeaf020ad68e3bd9722dd272357
isn't correct anymore:

length: size of the image. If negative, the API will try to figure out the
        length of the image

        NO, IT WILL NOT! It bails out with an error instead.
        Introduced a function to obtain the length for each collator data.

base:  collator, usually root. The base is required to be present through the
       lifetime of the collator. Currently it cannot be NULL.

       NOT "usually root"! There's a check now that bails out if
       if(base->tailoring != CollationRoot::getRoot(errorCode))
       So using an instance created with icu::Locale::getRoot()

Change-Id: Ia9c4e27d5ef4f8083bbe57e4e2f4b3ff63bb42ed