Fix smart_search_prefix handling of empty search
Fix smart_search_prefix handling of empty search

shlex.split() returns zero-length list for empty string input. As we
need something to iterate over to return a proper dict-SQL, this broke
things and so this manually fixes that by checking the result of
shlex.split()

Part of #259

plajjan/NIPAP,plajjan/NIPAP,ettrig/NIPAP,bbaja42/NIPAP,SoundGoof/NIPAP,bbaja42/NIPAP,plajjan/NIPAP,bbaja42/NIPAP,garberg/NIPAP,fredsod/NIPAP,SoundGoof/NIPAP,ettrig/NIPAP,fredsod/NIPAP,bbaja42/NIPAP,SpriteLink/NIPAP,bbaja42/NIPAP,SpriteLink/NIPAP,garberg/NIPAP,SoundGoof/NIPAP,SpriteLink/NIPAP,garberg/NIPAP,SpriteLink/NIPAP,bbaja42/NIPAP,SpriteLink/NIPAP,fredsod/NIPAP,plajjan/NIPAP,ettrig/NIPAP,garberg/NIPAP,SoundGoof/NIPAP,garberg/NIPAP,garberg/NIPAP,plajjan/NIPAP,fredsod/NIPAP,SpriteLink/NIPAP,ettrig/NIPAP,SoundGoof/NIPAP,SoundGoof/NIPAP,ettrig/NIPAP,fredsod/NIPAP,ettrig/NIPAP,fredsod/NIPAP,plajjan/NIPAP