Fix string buffer overwrite

Fix string buffer overwrite

std::string uses static buffer for empty string values. When
std::transform iterates over initialized std::string elements
and copies their changed values to empty std::string by using
its random access iterator, the buffer which is used by
std::string for empty strings is overriden, what later makes
all strings, that are supposed to be empty, not empty.

Change-Id: I5acb9e038febabbf4b1e1d56d736f75dc227c0af