patch 8.0.1381: ch_readraw() waits for NL if channel mode is NL

Problem:    ch_readraw() waits for NL if channel mode is NL.
Solution:   Pass a "raw" flag to channel_read_block(). (Yasuhiro Matsumoto)
diff --git a/src/testdir/test_channel_pipe.py b/src/testdir/test_channel_pipe.py
index a67a81a..9403786 100644
--- a/src/testdir/test_channel_pipe.py
+++ b/src/testdir/test_channel_pipe.py
@@ -14,6 +14,10 @@
         if sys.argv[1].startswith("err"):
             print(sys.argv[1], file=sys.stderr)
             sys.stderr.flush()
+        elif sys.argv[1].startswith("incomplete"):
+            print(sys.argv[1], end='')
+            sys.stdout.flush()
+            sys.exit(0)
         else:
             print(sys.argv[1])
             sys.stdout.flush()