Fix NPE in TransformerTranscodingVideoRenderer

The NPE was caused by the fact that the encoder surface was passed to
the decoder before configuring the encoder.

PiperOrigin-RevId: 393349794

library/transformer/src/main/java/com/google/android/exoplayer2/transformer/TransformerTranscodingVideoRenderer.java

@@ -69,14 +69,12 @@ import java.nio.ByteBuffer;
       return;
     }
 
-    if (!ensureDecoderConfigured()) {
+    if (!ensureEncoderConfigured() || !ensureDecoderConfigured()) {
       return;
     }
 
-    if (ensureEncoderConfigured()) {
+    while (feedMuxerFromEncoder()) {}
-      while (feedMuxerFromEncoder()) {}
+    while (feedEncoderFromDecoder()) {}
-      while (feedEncoderFromDecoder()) {}
-    }
     while (feedDecoderFromInput()) {}
   }