fix some small bugs with GrAtlasTextContext

src/gpu/GrAtlasTextContext.h

Index: src/gpu/GrAtlasTextContext.h
diff --git a/src/gpu/GrAtlasTextContext.h b/src/gpu/GrAtlasTextContext.h
index d294126799815284d35e135455263b6d440ccb78..c0975b9857df5c583dd9eeb41e3095d2fee9be58 100644
--- a/src/gpu/GrAtlasTextContext.h
+++ b/src/gpu/GrAtlasTextContext.h
@@ -248,7 +248,7 @@ private:
         uint8_t fTextType;
 
         BitmapTextBlob()
-            : fMaxMinScale(SK_ScalarMax)
+            : fMaxMinScale(-SK_ScalarMax)
             , fMinMaxScale(SK_ScalarMax)
             , fTextType(0) {}