lib: Add a null guard

get_event_config() can cause a segfault if NULL is passed to it, since
GHashTable tries to hash the pointer as a string.

Reproducible just by switching to the “Confirm data to report” tab
manually.

Signed-off-by: Ernestas Kulik <ekulik@redhat.com>

src/lib/event_config.c

@@ -310,6 +310,9 @@ void free_event_config_data(void)
 
 event_config_t *get_event_config(const char *name)
 {
+    if (name == NULL)
+        return NULL;
+
     if (!g_event_config_list)
         return NULL;
     if (g_event_config_symlinks)