Avoid IllegalArgumentException in GifFrameLoader.

IllegalArgumentException is thrown when the target is invisible and
startFromFirstFrame is called and the target subsequently becomes visible.

library/src/main/java/com/bumptech/glide/load/resource/gif/GifFrameLoader.java

@@ -268,7 +268,11 @@ void onFrameReady(DelayTarget delayTarget) {
     // already incremented the frame pointer and can't decode the same frame again. Instead we'll
     // just hang on to this next frame until start() or clear() are called.
     if (!isRunning) {
-      pendingTarget = delayTarget;
+      if (startFromFirstFrame) {
+        handler.obtainMessage(FrameLoaderCallback.MSG_CLEAR, delayTarget).sendToTarget();
+      } else {
+        pendingTarget = delayTarget;
+      }
       return;
     }
 

library/test/src/test/java/com/bumptech/glide/load/resource/gif/GifFrameLoaderTest.java

@@ -338,6 +338,18 @@ public void onFrameReady_whenNotRunning_callsFrameReadyWithNewFrameOnStart() {
     assertThat(loader.getCurrentFrame()).isEqualTo(expected);
   }
 
+  @Test
+  public void onFrameReady_whenInvisible_setVisibleLater() {
+    loader = createGifFrameLoader(/*handler=*/ null);
+    // The target is invisible at this point.
+    loader.unsubscribe(callback);
+    loader.setNextStartFromFirstFrame();
+    DelayTarget loaded = mock(DelayTarget.class);
+    when(loaded.getResource()).thenReturn(Bitmap.createBitmap(100, 100, Bitmap.Config.ARGB_8888));
+    loader.onFrameReady(loaded);
+    loader.subscribe(callback);
+  }
+
   @Test
   public void startFromFirstFrame_withPendingFrame_clearsPendingFrame() {
     loader = createGifFrameLoader(/*handler=*/ null);