To Reproduce.
1. Open the attached project & "loader" scene.
2. Press Play. Stop. Press Play again. Stop again.
3. The Editor should crash here:

Unity`UnityWebStream::GetFileStream(this=0xdeadbeef) + 15 at UnityWebStream.h:191, stop reason = EXC_BAD_ACCESS (code=1, address=0xdeadbf73)
frame #0: 0x00e25a7b Unity`UnityWebStream::GetFileStream(this=0xdeadbeef) + 15 at UnityWebStream.h:191
frame #1: 0x00f06fbf Unity`UnloadAssetBundle(file=0x112021b0, unloadAllLoadedObjects=true) + 95 at SaveAndLoadHelper.cpp:1105
frame #2: 0x01d7ba2c Unity`Application::SetIsPlaying(this=0x07f445c0, isPlaying=false) + 3154 at Application.cpp:2445
frame #3: 0x01d82432 Unity`Application::TickTimer(this=0x07f445c0) + 4994 at Application.cpp:1312
frame #4: 0x020861a4 Unity`-[EditorApplication TickTimer](self=0x0d31bdc0, _cmd=0x0250ac13) + 36 at EditorApplication.mm:323