Check input param consistently in FPDFPageObjMark_*.

Consistently convert the input FPDF_PAGEOBJECTMARK parameter using
CPDFContentMarkItemFromFPDFPageObjectMark(), and then check the
CPDF_ContentMarkItem pointer.

Change-Id: Id38f7c04d114120b46cdc27de2e069e7d4815fdb
Reviewed-on: https://pdfium-review.googlesource.com/c/pdfium/+/70475
Reviewed-by: Daniel Hosseinian <dhoss@chromium.org>
Commit-Queue: Lei Zhang <thestig@chromium.org>

fpdfsdk/fpdf_editpage.cpp

diff --git a/fpdfsdk/fpdf_editpage.cpp b/fpdfsdk/fpdf_editpage.cpp
index eb27a51..9c0a83a 100644
--- a/fpdfsdk/fpdf_editpage.cpp
+++ b/fpdfsdk/fpdf_editpage.cpp
@@ -345,11 +345,10 @@
                         void* buffer,
                         unsigned long buflen,
                         unsigned long* out_buflen) {
-  if (!mark || !out_buflen)
-    return false;
-
   const CPDF_ContentMarkItem* pMarkItem =
       CPDFContentMarkItemFromFPDFPageObjectMark(mark);
+  if (!pMarkItem || !out_buflen)
+    return false;
 
   *out_buflen = Utf16EncodeMaybeCopyAndReturnLength(
       WideString::FromUTF8(pMarkItem->GetName().AsStringView()), buffer,
@@ -359,11 +358,10 @@
 
 FPDF_EXPORT int FPDF_CALLCONV
 FPDFPageObjMark_CountParams(FPDF_PAGEOBJECTMARK mark) {
-  if (!mark)
-    return -1;
-
   const CPDF_ContentMarkItem* pMarkItem =
       CPDFContentMarkItemFromFPDFPageObjectMark(mark);
+  if (!pMarkItem)
+    return -1;
 
   const CPDF_Dictionary* pParams = pMarkItem->GetParam();
   return pParams ? pParams->size() : 0;