Create empty view for SplashScreenViewProvider#iconView if needed

There can return nullable for SplashScreenView#getIconView, which
allow developers to customize exit animation for solid color splash
screen.

Bug: 243457485
Test: SplashscreenParametrizedTest SplashScreenTests

Change-Id: I4c323d4f9307af9759da548dcadcd7b8318ecf60
diff --git a/core/core-splashscreen/src/main/java/androidx/core/splashscreen/SplashScreenViewProvider.kt b/core/core-splashscreen/src/main/java/androidx/core/splashscreen/SplashScreenViewProvider.kt
index 8a5a9e4..3fc305c 100644
--- a/core/core-splashscreen/src/main/java/androidx/core/splashscreen/SplashScreenViewProvider.kt
+++ b/core/core-splashscreen/src/main/java/androidx/core/splashscreen/SplashScreenViewProvider.kt
@@ -122,7 +122,8 @@
 
         override val splashScreenView get() = platformView
 
-        override val iconView get() = platformView.iconView!!
+        override val iconView: View
+            get() = if (platformView.iconView != null) platformView.iconView!! else View(activity)
 
         override val iconAnimationStartMillis: Long
             get() = platformView.iconAnimationStart?.toEpochMilli() ?: 0