Tar reader stuck with certain files and chunk sizes (#2698)

Cannot share repeating tar files but when reading certain tar files the stage would get stuck waiting
for more data to be pushed but without having pulled upstream to actually get the next chunk.

file/src/main/scala/akka/stream/alpakka/file/impl/archive/TarReaderStage.scala

@@ -5,7 +5,6 @@
 package akka.stream.alpakka.file.impl.archive
 
 import java.util.concurrent.TimeUnit
-
 import akka.NotUsed
 import akka.annotation.InternalApi
 import akka.stream.ActorAttributes.StreamSubscriptionTimeout
@@ -37,12 +36,15 @@ private[file] class TarReaderStage
           extends SubSourceOutlet[ByteString]("fileOut")
           with TarReaderStage.SourceWithTimeout
 
-      readHeader(ByteString.empty)
+      setHandlers(flowIn, flowOut, new CollectHeader(ByteString.empty))
 
       def readHeader(buffer: ByteString): Unit = {
         if (buffer.length >= TarArchiveEntry.headerLength) {
           readFile(buffer)
-        } else setHandlers(flowIn, flowOut, new CollectHeader(buffer))
+        } else {
+          if (!hasBeenPulled(flowIn)) pull(flowIn)
+          setHandlers(flowIn, flowOut, new CollectHeader(buffer))
+        }
       }
 
       def readFile(headerBuffer: ByteString): Unit = {