Fix Bangumi tracker losing track of login expiration (#1681)

* Fix Bangumi tracking losing track of login state

kotlinx.serialization does NOT serialize default values (like
createdAt in BGMOAuth.kt), so every time the Bangumi tracker
deserialized the tracker OAuth, createdAt was set to the time of the
read, not the time of issuance.

Separately, BangumiInterceptor did correctly fetch new OAuth
credentials upon detected expiry of the stored credentials and saved
them, but did not use them for the current request (the new
credentials were used for all subsequent requests only). This led to
401 errors from Bangumi because the expired access_token was provided.
 A subsequent request using the newly acquired access_token would end
 up being successful.

* Add CHANGELOG.md entry

CHANGELOG.md

@@ -17,6 +17,7 @@ The format is a modified version of [Keep a Changelog](https://keepachangelog.co
 
 ### Fixed
 - Fix MAL `main_picture` nullability breaking search if a result doesn't have a cover set ([@MajorTanya](https://github.com/MajorTanya)) ([#1618](https://github.com/mihonapp/mihon/pull/1618))
+- Fix Bangumi tracking 401 errors due to Mihon sending expired credentials ([@MajorTanya](https://github.com/MajorTanya)) ([#1681](https://github.com/mihonapp/mihon/pull/1681))
 
 ### Other
 - Add zoned "Current time" to debug info and include year & timezone in logcat output ([@MajorTanya](https://github.com/MajorTanya)) ([#1672](https://github.com/mihonapp/mihon/pull/1672))

app/src/main/java/eu/kanade/tachiyomi/data/track/bangumi/BangumiInterceptor.kt

@@ -21,12 +21,13 @@ class BangumiInterceptor(private val bangumi: Bangumi) : Interceptor {
     override fun intercept(chain: Interceptor.Chain): Response {
         val originalRequest = chain.request()
 
-        val currAuth = oauth ?: throw Exception("Not authenticated with Bangumi")
+        var currAuth: BGMOAuth = oauth ?: throw Exception("Not authenticated with Bangumi")
 
         if (currAuth.isExpired()) {
             val response = chain.proceed(BangumiApi.refreshTokenRequest(currAuth.refreshToken!!))
             if (response.isSuccessful) {
-                newAuth(json.decodeFromString<BGMOAuth>(response.body.string()))
+                currAuth = json.decodeFromString<BGMOAuth>(response.body.string())
+                newAuth(currAuth)
             } else {
                 response.close()
             }

app/src/main/java/eu/kanade/tachiyomi/data/track/bangumi/dto/BGMOAuth.kt

@@ -1,5 +1,6 @@
 package eu.kanade.tachiyomi.data.track.bangumi.dto
 
+import kotlinx.serialization.EncodeDefault
 import kotlinx.serialization.SerialName
 import kotlinx.serialization.Serializable
 
@@ -10,6 +11,7 @@ data class BGMOAuth(
     @SerialName("token_type")
     val tokenType: String,
     @SerialName("created_at")
+    @EncodeDefault
     val createdAt: Long = System.currentTimeMillis() / 1000,
     @SerialName("expires_in")
     val expiresIn: Long,