Android: Allow SurfaceTextureHelper.textureToYuv to be used for RGB frames

TBR=sakal@webrtc.org

Bug: b/69162554
Change-Id: I342777a1cc961346a3e61408d02fbc6a16b7b633
Reviewed-on: https://webrtc-review.googlesource.com/24101
Reviewed-by: Magnus Jedvert <magjed@webrtc.org>
Commit-Queue: Magnus Jedvert <magjed@webrtc.org>
Cr-Commit-Position: refs/heads/master@{#20748}

sdk/android/api/org/webrtc/YuvConverter.java

@@ -216,6 +216,7 @@ public class YuvConverter {
     if (textureType != shaderTextureType) {
       initShader(textureType);
     }
+    shader.useProgram();
 
     // We draw into a buffer laid out like
     //