fix test for empty config

handle empty setconfig

BUG=skia:

Review URL: https://codereview.chromium.org/159533002

git-svn-id: http://skia.googlecode.com/svn/trunk@13394 2bbb7eff-a529-9590-31e7-b0007b416f81

src/core/SkBitmap.cpp

@@ -263,7 +263,7 @@ bool SkBitmap::setConfig(const SkImageInfo& info, size_t rowBytes) {
         return reset_return_false(this);
     }
 
-    if (info.isEmpty()) {
+    if (info.width() < 0 || info.height() < 0) {
         return reset_return_false(this);
     }