Do not hang on full PTY

Signed-off-by: Don Slutz <dslutz@verizon.com>
Reviewed-by: Paolo Bonzini <pbonzini@redhat.com>
Signed-off-by: Michael Tokarev <mjt@tls.msk.ru>
diff --git a/qemu-char.c b/qemu-char.c
index 5430b87..98d4342 100644
--- a/qemu-char.c
+++ b/qemu-char.c
@@ -1402,6 +1402,7 @@
     }
 
     close(slave_fd);
+    qemu_set_nonblock(master_fd);
 
     chr = qemu_chr_alloc();