Call isEmpty() instead of constructing a new object to compare

A recent change in Skia
(https://skia-review.googlesource.com/c/skia/+/573636) moves operator==
into the cpp file, where this file cannot access it due to libhwui's map
file. Call isEmpty, which is still in the header file, and skips
unnecessary creation of a new object anyway.

Bug: NA
Test: AImageDecoderTest
Change-Id: I1dec89a38e248138ace364e8cb7259eb777e8871
diff --git a/native/graphics/jni/imagedecoder.cpp b/native/graphics/jni/imagedecoder.cpp
index cd6ed23..7fe2735 100644
--- a/native/graphics/jni/imagedecoder.cpp
+++ b/native/graphics/jni/imagedecoder.cpp
@@ -381,7 +381,7 @@
 
     SkIRect cropIRect;
     cropIRect.setLTRB(crop.left, crop.top, crop.right, crop.bottom);
-    SkIRect* cropPtr = cropIRect == SkIRect::MakeEmpty() ? nullptr : &cropIRect;
+    SkIRect* cropPtr = cropIRect.isEmpty() ? nullptr : &cropIRect;
     return imageDecoder->setCropRect(cropPtr)
             ? ANDROID_IMAGE_DECODER_SUCCESS : ANDROID_IMAGE_DECODER_BAD_PARAMETER;
 }