(dump): Correct loop-termination criterion.

Before, running `printf 1234| ./od --width=4 --read-bytes=4'
printed output for 8 bytes -- the last four were garbage.
This happened only when the dump limit, N, was specified (with
--read-bytes=N) and N was a multiple of bytes_per_block
(usually 16, but 4 in this example).  From Andreas Schwab.

1 files changed, 6 insertions, 2 deletions

diff --git a/src/od.c b/src/od.c
index ffce0d6a0..28fdc66d4 100644
--- a/src/od.c
+++ b/src/od.c
@@ -1397,12 +1397,16 @@ dump ()
     {
       end_offset = n_bytes_to_skip + max_bytes_to_format;
 
-      n_bytes_read = 0;
-      while (current_offset < end_offset)
+      while (1)
 	{
 	  size_t n_needed;
 	  n_needed = MIN (end_offset - current_offset,
 			  (off_t) bytes_per_block);
+	  if (n_needed == 0)
+	    {
+	      n_bytes_read = 0;
+	      break;
+	    }
 	  err |= read_block (n_needed, block[idx], &n_bytes_read);
 	  if (n_bytes_read < bytes_per_block)
 	    break;