Fix handling of empty array directives in the SDLang recipe parser.
Fix handling of empty array directives in the SDLang recipe parser.

A directive such as "sourcePaths" didn't result in an empty array entry to be inserted into the build settings, which in turn caused the package loading code to still search for the default source paths.

D-Programming-Language/dub,jeanbaptistelab/dub,grogancolin/dub,rjframe/dub,Geod24/dub,gedaiu/dub,Flamaros/dub,p0nce/dub