Use WideStringFromFPDFWideString() in more places.

Also rename CFXByteStringFromFPDFWideString() to
ByteStringFromFPDFWideString(), and implement it using
WideStringFromFPDFWideString().

Change-Id: I323bf69f90cdec78bbee562b9aed6513599c9e33
Reviewed-on: https://pdfium-review.googlesource.com/c/47692
Commit-Queue: Lei Zhang <thestig@chromium.org>
Reviewed-by: Tom Sepez <tsepez@chromium.org>
diff --git a/fpdfsdk/fpdf_attachment.cpp b/fpdfsdk/fpdf_attachment.cpp
index de7389d..3db89a8 100644
--- a/fpdfsdk/fpdf_attachment.cpp
+++ b/fpdfsdk/fpdf_attachment.cpp
@@ -59,15 +59,17 @@
 FPDF_EXPORT FPDF_ATTACHMENT FPDF_CALLCONV
 FPDFDoc_AddAttachment(FPDF_DOCUMENT document, FPDF_WIDESTRING name) {
   CPDF_Document* pDoc = CPDFDocumentFromFPDFDocument(document);
-  WideString wsName =
-      WideString::FromUTF16LE(name, WideString::WStringLength(name));
-  if (!pDoc || wsName.IsEmpty())
+  if (!pDoc)
     return nullptr;
 
   CPDF_Dictionary* pRoot = pDoc->GetRoot();
   if (!pRoot)
     return nullptr;
 
+  WideString wsName = WideStringFromFPDFWideString(name);
+  if (wsName.IsEmpty())
+    return nullptr;
+
   // Retrieve the document's Names dictionary; create it if missing.
   CPDF_Dictionary* pNames = pRoot->GetDictFor("Names");
   if (!pNames) {
@@ -170,7 +172,7 @@
     return false;
 
   ByteString bsKey = key;
-  ByteString bsValue = CFXByteStringFromFPDFWideString(value);
+  ByteString bsValue = ByteStringFromFPDFWideString(value);
   bool bEncodedAsHex = bsKey == kChecksumKey;
   if (bEncodedAsHex)
     bsValue = CFXByteStringHexDecode(bsValue);