Parsing malformed HLS causes crash

(Note: Found in 1.x but should also check 2.x when fixing)

Parsing this playlist:

```
#EXTM3U
#EXT-X-VERSION:7
#EXT-X-PLAYLIST-TYPE:EVENT
#EXT-X-TARGETDURATION:3
#EXT-X-KEY:METHOD=AES-128,URI="http://myserver.com",IV=0x000102030aaaaccccccccbbbbb0d0e0f
#EXT-X-MAP:URI=\"http://myserver.com/init.mp4\"
#EXT-X-ENDLIST
```

### Expected Behavior

Parse should succeed

### Observed Behavior

Crash in `HLSPlaylistStructure.rebuild()`

### Observed on device(s):

* All devices

### Observed on OS Version(s):

* iOS 13.2