made SEBIOS not crash when there's an empty tape drive present

sebios.lua

@@ -72,9 +72,9 @@ do
   end
   wl("SKS Enhanced BIOS v1")
   wl("Memory: "..tostring(computer.totalMemory()/1024).."K")
-  wl("")
+  wl(" ")
   for k,v in ipairs(bootdevs) do
-   wl(tostring(k-1).." "..v.." "..component.type(v).." "..component.invoke(v,"getLabel"))
+   wl(tostring(k-1).." "..v.." "..component.type(v).." "..(component.invoke(v,"getLabel") or ""))
   end
   local timer = 5
   while computer.uptime() < timer do