not a failure if we didn't load the test file

BUG=skia:

Review URL: https://codereview.chromium.org/687453005
diff --git a/tests/KtxTest.cpp b/tests/KtxTest.cpp
index 1a61f3a..499db6a 100644
--- a/tests/KtxTest.cpp
+++ b/tests/KtxTest.cpp
@@ -145,8 +145,8 @@
     // Load PKM file into a bitmap
     SkBitmap etcBitmap;
     SkAutoTUnref<SkData> fileData(SkData::NewFromFileName(pkmFilename.c_str()));
-    REPORTER_ASSERT(reporter, fileData);
     if (NULL == fileData) {
+        SkDebugf("KtxReexportPKM: can't load test file %s\n", pkmFilename.c_str());
         return;
     }