Cannot upload video to unencrypted v6 rooms.

From Element iOS v1.0.2 build 20200728141906 I cannot upload videos to unencrypted v6 rooms. I did a rage shake about a half hour ago with a screen cap and logs.

I'm also including the Synapse server logs. It looks like Element iOS is trying to send the server a JSON float value when it's not expected, probably expecting an int value.

```
2020-08-17 18:00:15,898 - synapse.http.server - 74 - INFO - PUT-549277 - SynapseError: 400 - Bad JSON value: float
2020-08-17 18:00:15,899 - synapse.access.https.8008 - 310 - INFO - PUT-549277 - 10.X.Y.Z - 8008 - {@:} Processed request: 0.006sec/0.000sec (0.005sec, 0.000sec) (0.001sec/0.002sec/2) 70B 400 "PUT /_matrix/client/r0/rooms/!:/send/m.room.message/kMXEventLocalId_ HTTP/1.0" "Riot/1.0.2 (iPhone; iOS 13.6; Scale/2.00)" [0 dbevts]
```

This issues seems similar to another issue with Element Android where int values are being sent as float values to Synapse when images are being uploaded. https://github.com/vector-im/element-android/issues/1879