fix deserializing null focus values

[connyduck]

Found a post with this weird media focus in the wild on chaos.social:

"focus": {
    "x": 0.0,
    "y": null
}

com.squareup.moshi.JsonDataException: Expected a double but was NULL at path $[0].media_attachments[0].meta.focus.y
         at com.squareup.moshi.JsonUtf8Reader.nextDouble(JsonUtf8Reader.java:787)
         at com.squareup.moshi.StandardJsonAdapters$6.fromJson(StandardJsonAdapters.java:167)
         at com.squareup.moshi.StandardJsonAdapters$6.fromJson(StandardJsonAdapters.java:164)
         at com.keylesspalace.tusky.entity.Attachment_FocusJsonAdapter.fromJson(Attachment_FocusJsonAdapter.kt:37)
         at com.keylesspalace.tusky.entity.Attachment_FocusJsonAdapter.fromJson(Attachment_FocusJsonAdapter.kt:20)
         at com.squareup.moshi.internal.NullSafeJsonAdapter.fromJson(NullSafeJsonAdapter.java:41)
         at com.keylesspalace.tusky.entity.Attachment_MetaDataJsonAdapter.fromJson(Attachment_MetaDataJsonAdapter.kt:54)
         at com.keylesspalace.tusky.entity.Attachment_MetaDataJsonAdapter.fromJson(Attachment_MetaDataJsonAdapter.kt:23)
         at com.squareup.moshi.internal.NullSafeJsonAdapter.fromJson(NullSafeJsonAdapter.java:41)
         at com.keylesspalace.tusky.entity.AttachmentJsonAdapter.fromJson(AttachmentJsonAdapter.kt:66)
         at com.keylesspalace.tusky.entity.AttachmentJsonAdapter.fromJson(AttachmentJsonAdapter.kt:22)
         at com.squareup.moshi.internal.NullSafeJsonAdapter.fromJson(NullSafeJsonAdapter.java:41)
         at com.squareup.moshi.CollectionJsonAdapter.fromJson(CollectionJsonAdapter.java:81)
         at com.squareup.moshi.CollectionJsonAdapter$2.fromJson(CollectionJsonAdapter.java:55)
         at com.squareup.moshi.internal.NullSafeJsonAdapter.fromJson(NullSafeJsonAdapter.java:41)
         at com.keylesspalace.tusky.entity.StatusJsonAdapter.fromJson(StatusJsonAdapter.kt:195)
         at com.keylesspalace.tusky.entity.StatusJsonAdapter.fromJson(StatusJsonAdapter.kt:26)
         at com.squareup.moshi.internal.NullSafeJsonAdapter.fromJson(NullSafeJsonAdapter.java:41)
         at com.squareup.moshi.CollectionJsonAdapter.fromJson(CollectionJsonAdapter.java:81)
         at com.squareup.moshi.CollectionJsonAdapter$2.fromJson(CollectionJsonAdapter.java:55)
         at com.squareup.moshi.internal.NullSafeJsonAdapter.fromJson(NullSafeJsonAdapter.java:41)
         at retrofit2.converter.moshi.MoshiResponseBodyConverter.convert(MoshiResponseBodyConverter.java:46)
         at retrofit2.converter.moshi.MoshiResponseBodyConverter.convert(MoshiResponseBodyConverter.java:27)
         at retrofit2.OkHttpCall.parseResponse(OkHttpCall.java:246)
         at retrofit2.OkHttpCall$1.onResponse(OkHttpCall.java:156)
         at okhttp3.internal.connection.RealCall$AsyncCall.run(RealCall.kt:519)
         at java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1167)
         at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:641)
         at java.lang.Thread.run(Thread.java:919)

[connyduck]

The post in question: https://mstdn.party/@Woodswalked/111394374883623726