extcap: Remove single-space argument for boolflags

 Boolflags will be added with a NULL argument to the
 list and therefore the original fix will work.

 Note: extcap_get_complex_as_string will convert any NULL
 value into a single character argument (' '). Therefore
 any argument type, where NULL is a special value should
 be handled seperately here. For now, the only datatype
 will be BOOLFLAG

Change-Id: Icfc9b573214e05ea713a3b70ea37953d470dafae
Reviewed-on: https://code.wireshark.org/review/4649Reviewed-by: Roland Knall <rknall@gmail.com>
Reviewed-by: Tomasz Moń <desowin@gmail.com>
Reviewed-by: Pascal Quantin <pascal.quantin@gmail.com>

ui/gtk/extcap_gtk.c

@@ -316,10 +316,10 @@ GHashTable *extcap_gtk_get_state(GtkWidget *widget) {
              */
             if (extcap_compare_is_default(arg, parsed_complex))
                 continue;
-        }
 
-        if (parsed_complex != NULL && call_string == NULL)
-            call_string = extcap_get_complex_as_string(parsed_complex);
+            if (parsed_complex != NULL && call_string == NULL)
+                call_string = extcap_get_complex_as_string(parsed_complex);
+        }
 
         g_hash_table_insert(ret_hash, g_strdup(arg->call),
                 g_strdup(call_string));