Rename CXFA_Value methods for clarity

This CL marks the methods in CXFA_Value to make it clear which can
return nullptr and updates callsites as needed.

Change-Id: If1f794bcbbddaa57a1efdd67195df58a77b4373a
Reviewed-on: https://pdfium-review.googlesource.com/22773
Commit-Queue: dsinclair <dsinclair@chromium.org>
Reviewed-by: Ryan Harrison <rharrison@chromium.org>
diff --git a/xfa/fxfa/cxfa_ffrectangle.cpp b/xfa/fxfa/cxfa_ffrectangle.cpp
index b3dd6f4..46c1009 100644
--- a/xfa/fxfa/cxfa_ffrectangle.cpp
+++ b/xfa/fxfa/cxfa_ffrectangle.cpp
@@ -31,5 +31,5 @@
   CFX_Matrix mtRotate = GetRotateMatrix();
   mtRotate.Concat(matrix);
 
-  DrawBorder(pGS, value->GetRectangle(), rect, mtRotate);
+  DrawBorder(pGS, value->GetRectangleIfExists(), rect, mtRotate);
 }