[Media3][Shader] Reset the composite RGB matrix upon update

Since the composite matrix is ultimately rewritten to, we need to ensure it's cleared (to identity) before update.

Test plan: use an effect as a time based approach and see that the effect no longer clips

PiperOrigin-RevId: 518886623

library/effect/src/main/java/com/google/android/exoplayer2/effect/DefaultShaderProgram.java

@@ -535,6 +535,8 @@ import java.util.List;
       return;
     }
 
+    GlUtil.setToIdentity(compositeRgbMatrixArray);
+
     for (int i = 0; i < rgbMatrices.size(); i++) {
       Matrix.multiplyMM(
           /* result= */ tempResultMatrix,