Fix build of skin_generator: no explicit QString->QDir conversation
Fix build of skin_generator: no explicit QString->QDir conversation

If code compiles with "-DQT_USE_QSTRINGBUILDER" (for more fast QString
concantation) then code with implicit QString -> QDir conversation
cause compile time error.

mapsme/omim,mapsme/omim,mapsme/omim,mapsme/omim,mpimenov/omim,mapsme/omim,mapsme/omim,mpimenov/omim,mapsme/omim,mapsme/omim,mpimenov/omim,mpimenov/omim,mpimenov/omim,mpimenov/omim,mpimenov/omim,mpimenov/omim,mapsme/omim,mpimenov/omim,mpimenov/omim,mapsme/omim,mpimenov/omim,mapsme/omim,mapsme/omim,mpimenov/omim,mapsme/omim,mpimenov/omim