fix use of uninitialized flag in SkCodec

SkCodec class has the fStartedIncrementalDecode field, which is not
initialized on construction, but may be used in incrementalDecode
method being uninitialized.

Bug: skia:
Change-Id: I378412a375100ad2df4aa38f2dd5682867e0e34b
Reviewed-on: https://skia-review.googlesource.com/53160
Commit-Queue: Heather Miller <hcm@google.com>
Reviewed-by: Mike Klein <mtklein@google.com>
Reviewed-by: Mike Klein <mtklein@chromium.org>
diff --git a/AUTHORS b/AUTHORS
index f4b36aa..6def302 100644
--- a/AUTHORS
+++ b/AUTHORS
@@ -22,6 +22,7 @@
 Igalia <*@igalia.com>
 Intel <*@intel.com>
 Ion Rosca <rosca@adobe.com>
+Ivan Afanasyev <ivafanas@yandex-team.ru>
 Jacek Caban <cjacek@gmail.com>
 Jeff Muizelaar <jmuizelaar@mozilla.com>
 Lee Salzman <lsalzman@mozilla.com>