rx: fix file corruption on block checksum failure

Rather than dropping the bad block, rx was appending it
to the file.

Signed-off-by: Daniel Fandrich <dan@coneharvesters.com>
Signed-off-by: Denys Vlasenko <vda.linux@googlemail.com>
diff --git a/miscutils/rx.c b/miscutils/rx.c
index c48a61f..af59732 100644
--- a/miscutils/rx.c
+++ b/miscutils/rx.c
@@ -207,6 +207,7 @@
 		continue;
  error:
  timeout:
+		blockLength = 0;
 		errors++;
 		if (errors == MAXERRORS) {
 			/* Abort */