extcap: fix a crash introduced in g622603b

When using GTK UI, cfilter is initialized to NULL, not to an empty string.

Change-Id: Ic9f3957d4de551a929578e76d5b9c63936517299
Reviewed-on: https://code.wireshark.org/review/11910
Reviewed-by: Pascal Quantin <pascal.quantin@gmail.com>

1 files changed, 1 insertions, 1 deletions

diff --git a/extcap.c b/extcap.c
index c161e48c39..22fdb7553d 100644
--- a/extcap.c
+++ b/extcap.c
@@ -583,7 +583,7 @@ extcaps_init_initerfaces(capture_options *capture_opts)
         add_arg(EXTCAP_ARGUMENT_RUN_CAPTURE);
         add_arg(EXTCAP_ARGUMENT_INTERFACE);
         add_arg(interface_opts.name);
-        if (strlen(interface_opts.cfilter) > 0) {
+        if (interface_opts.cfilter && strlen(interface_opts.cfilter) > 0) {
             add_arg(EXTCAP_ARGUMENT_CAPTURE_FILTER);
             add_arg(interface_opts.cfilter);
         }