Removed unnecessary null check on node prefix

Author: magneticflux-

src/main/kotlin/com/github/magneticflux/rss/Converters.kt

@@ -16,7 +16,7 @@ internal val InputNode.fullName: String
     get() {
         val prefix = this.prefix
         val name = this.name
-        return if (prefix.isNullOrEmpty()) name else "$prefix:$name"
+        return if (prefix.isEmpty()) name else "$prefix:$name"
     }
 
 /**
@@ -46,4 +46,4 @@ private class InputNodeChildIterator(val rootNode: InputNode) : AbstractIterator
             setNext(next)
         else done()
     }
-}
+}