Implement Fill() for incomplete decodes to RGBA_F16

Before this patch, we would hit an SkASSERT(false).

BUG=skia:
GOLD_TRYBOT_URL= https://gold.skia.org/search?issue=2335203002

Review-Url: https://codereview.chromium.org/2335203002
diff --git a/dm/DMSrcSink.cpp b/dm/DMSrcSink.cpp
index 6b33023..0c7de85 100644
--- a/dm/DMSrcSink.cpp
+++ b/dm/DMSrcSink.cpp
@@ -915,7 +915,7 @@
 
     size_t rowBytes = bitmap.rowBytes();
     SkCodec::Result r = codec->getPixels(decodeInfo, bitmap.getPixels(), rowBytes);
-    if (SkCodec::kSuccess != r) {
+    if (SkCodec::kSuccess != r && SkCodec::kIncompleteInput != r) {
         return SkStringPrintf("Couldn't getPixels %s. Error code %d", fPath.c_str(), r);
     }