Fix parsing of double dot operators for FormCalc

Patch by cherycherian.
patch from issue 1810153003 at patchset 1 (http://crrev.com/1810153003#ps1)

FormCalc expressions containing double-dot operators in SOM expressions
were failing since XFA_ResolveNodes_AnyChild was always stripping the
leading character.

Roll testing/corpus to d671154 to pick up the test.

BUG=pdfium:434
TBR=dsinclair@chromium.org

Review URL: https://codereview.chromium.org/1821413002 .
diff --git a/AUTHORS b/AUTHORS
index e8a89f7..cecbebf 100644
--- a/AUTHORS
+++ b/AUTHORS
@@ -11,6 +11,7 @@
 Andrey Khalyavin <halyavin@chromium.org>
 Brett Wilson <brettw@chromium.org>
 Bruce Dawson <brucedawson@chromium.org>
+Chery Cherian <cherycherian@gmail.com>
 Chris Palmer <palmer@chromium.org>
 Dan Sinclair <dsinclair@chromium.org>
 Finnur Thorarinsson <finnur@chromium.org>
@@ -31,5 +32,6 @@
 Sam Clegg <sbc@chromium.org>
 Thomas Sepez <tsepez@chromium.org>
 
+DocsCorp Pty Ltd. <*@docscorp.com>
 Foxit Software Inc <*@foxitsoftware.com>
 Google Inc. <*@google.com>