host/store: Fix null pointer dereference

If config_fcb reads an empty string it returns NULL pointer. We should handle this in ble_store_config module

Author: m-gorecki

nimble/host/store/config/src/ble_store_config_conf.c

@@ -91,6 +91,11 @@ ble_store_config_conf_set(int argc, char **argv, char *val)
 {
  int rc;
 
+ /* Config returns NULL pointer if it reads an empty string. We change this back into an empty string. */
+ if (!val) {
+ val = "";
+ }
+
  if (argc == 1) {
  if (strcmp(argv[0], "our_sec") == 0) {
  rc = ble_store_config_deserialize_arr(