nimble/controller: fix null pointer dereference
nimble/controller: fix null pointer dereference

X-Original-Commit: 3efb475d7077faff710844cf8b79602e8b0c8154

apache/mynewt-nimble,apache/mynewt-nimble,apache/mynewt-nimble,apache/mynewt-nimble,apache/mynewt-nimble