text: Fix handling of unbreakable-space in ssa subtitles

The character sequence \h is used for "unbreakable space".
Replace these sequences with space to avoid strings of \h
showing up on screen.

library/core/src/main/java/com/google/android/exoplayer2/text/ssa/SsaDecoder.java

@@ -264,7 +264,8 @@ public final class SsaDecoder extends SimpleSubtitleDecoder {
     String text =
         SsaStyle.Overrides.stripStyleOverrides(rawText)
             .replaceAll("\\\\N", "\n")
-            .replaceAll("\\\\n", "\n");
+            .replaceAll("\\\\n", "\n")
+            .replaceAll("\\\\h", " ");
     Cue cue = createCue(text, style, styleOverrides, screenWidth, screenHeight);
 
     int startTimeIndex = addCuePlacerholderByTime(startTimeUs, cueTimesUs, cues);