fix(android,ios): the player names the episode, not its file

The header under the episode's numbering showed `Episode::detail`, which
falls back to the file name — `[Judas] Chainsaw Man - S01E01.mkv` on a
phone, where the desktop shows `Dog & Chainsaw`. It now shows the
provider's name for the episode, else the one the file name gave it, and
nothing rather than the file name: the release group's tag is no caption,
and it is what a screenshot of the player would carry away.

ios/ProtonStream/UI/Common.swift

@@ -342,12 +342,19 @@ func downloadStatusLine(_ download: RetainedDownload, waitingFor: String? = nil)
 }
 
 extension EpisodeRecord {
+    /// The episode's own name: the provider's, else the one the filename gave
+    /// it. `nil` rather than the filename, which is a release group's tag and
+    /// the episode's numbering again.
+    var shownName: String? {
+        providerName ?? (detail != name && !detail.isEmpty ? detail : nil)
+    }
+
     /// What an episode row is headed with: "1. Mother and Children".
     ///
     /// The provider's name for the episode, else the name the filename gave it,
     /// else "Episode 1". The bare filename only when none of those exist.
     func heading(_ position: Int) -> String {
-        let named = providerName ?? (detail != name ? detail : nil)
+        let named = shownName
         switch (named, number) {
         case let (named?, number?): return "\(number). \(named)"
         case let (named?, nil): return named