Fix for output directory creation (#21)

src/main/scala/millfork/Main.scala

@@ -76,6 +76,7 @@ object Main {
     }
 
     val outputParent = new File(output).getParentFile
+    if (outputParent ne null) {
       if (outputParent.exists()) {
         if (!outputParent.canWrite || !outputParent.isDirectory) {
           errorReporting.warn(s"The output directory `${outputParent.getAbsolutePath}` cannot be written to.")
@@ -85,6 +86,7 @@ object Main {
           errorReporting.warn(s"Failed to create the output directory `${outputParent.getAbsolutePath}``")
         }
       }
+    }
 
     val assOutput = output + ".asm"
 //    val prgOutputs = (platform.outputStyle match {