Mark some GetQuadPointsArrayFromDictionary() inputs const.

Const pointer in, const pointer out.

Change-Id: Ic4633a738ecd0cc1b06005e14e33d912a66c8c60
Reviewed-on: https://pdfium-review.googlesource.com/c/pdfium/+/52270
Reviewed-by: Tom Sepez <tsepez@chromium.org>
Commit-Queue: Lei Zhang <thestig@chromium.org>
diff --git a/fpdfsdk/fpdf_doc.cpp b/fpdfsdk/fpdf_doc.cpp
index 52e1e6b..e523321 100644
--- a/fpdfsdk/fpdf_doc.cpp
+++ b/fpdfsdk/fpdf_doc.cpp
@@ -374,7 +374,7 @@
   if (!quad_points || quad_index < 0)
     return false;
 
-  CPDF_Dictionary* pLinkDict = CPDFDictionaryFromFPDFLink(link_annot);
+  const CPDF_Dictionary* pLinkDict = CPDFDictionaryFromFPDFLink(link_annot);
   if (!pLinkDict)
     return false;