Initialize text_outfile to NULL.

'device' and 'outfile' are initialized from 'settings' in the later code,
but 'text_outfile' is not initialized, which may lead to writing to an unknown file.

src/main.c

@@ -130,7 +130,7 @@ int
 main(int argc, char* argv[])
 {
     int opt, idx, limit, only_calls, no_incomplete, pcap_buffer_size, i;
-    const char *device, *outfile, *text_outfile;
+    const char *device, *outfile, *text_outfile = NULL;
     char bpf[512];
 #if defined(WITH_GNUTLS) || defined(WITH_OPENSSL)
     const char *keyfile;