patch 8.1.0838: compiler warning for type conversion

Problem:    Compiler warning for type conversion.
Solution:   Add a type cast. (Mike Williams)
diff --git a/src/channel.c b/src/channel.c
index 7c649b1..4199398 100644
--- a/src/channel.c
+++ b/src/channel.c
@@ -90,7 +90,7 @@
 	if (todo > MAX_NAMED_PIPE_SIZE)
 	    size = MAX_NAMED_PIPE_SIZE;
 	else
-	    size = todo;
+	    size = (DWORD)todo;
 	// If the pipe overflows while the job does not read the data, WriteFile
 	// will block forever. This abandons the write.
 	memset(&ov, 0, sizeof(ov));