Format negative durations correctly

formatDuration() previously emitted strings like '00:-49' for negative
values because the modulo operations propagated the sign. This shows up
on live streams that briefly report a negative position during reload,
and as the basis for a planned 'behind live edge' indicator.

Recurse on the absolute value when negative so we get a clean -MM:SS
(or -HH:MM:SS) format.

app/src/main/java/com/futo/platformplayer/Extensions_Formatting.kt

@@ -251,6 +251,11 @@ fun String.fixHtmlWhitespace(): Spanned {
 }
 
 fun Long.formatDuration(): String {
+    // Negative durations show up for live streams seeked behind the seek-window start, or
+    // briefly while the player is reseating. Recurse on the absolute value so we get a clean
+    // `-MM:SS` instead of garbage like `00:-49`.
+    if (this < 0) return "-" + (-this).formatDuration()
+
     val hours = this / 3600000
     val minutes = (this % 3600000) / 60000
     val seconds = (this % 60000) / 1000