Add type cast definitions for CPDF_String.

core/src/fpdftext/fpdf_text_int.cpp

Index: core/src/fpdftext/fpdf_text_int.cpp
diff --git a/core/src/fpdftext/fpdf_text_int.cpp b/core/src/fpdftext/fpdf_text_int.cpp
index 99f36a08585e1002e74ff4f82eda544f6899e8d0..9ab09e19e44dab52fd3a2779ed6d525d95cfa4ae 100644
--- a/core/src/fpdftext/fpdf_text_int.cpp
+++ b/core/src/fpdftext/fpdf_text_int.cpp
@@ -1288,8 +1288,7 @@ int32_t CPDF_TextPage::PreMarkedContent(PDFTEXT_Obj Obj) {
     CFX_ByteString tagStr = (CFX_ByteString)item.GetName();
     pDict = ToDictionary(static_cast<CPDF_Object*>(item.GetParam()));
     CPDF_String* temp =
-        (CPDF_String*)(pDict ? pDict->GetElement(FX_BSTRC("ActualText"))
-                             : NULL);
+        ToString(pDict ? pDict->GetElement(FX_BSTRC("ActualText")) : nullptr);
     if (temp) {
       bExist = TRUE;
       actText = temp->GetUnicodeText();
@@ -1359,8 +1358,7 @@ void CPDF_TextPage::ProcessMarkedContent(PDFTEXT_Obj Obj) {
     CFX_ByteString tagStr = (CFX_ByteString)item.GetName();
     pDict = ToDictionary(static_cast<CPDF_Object*>(item.GetParam()));
     CPDF_String* temp =
-        (CPDF_String*)(pDict ? pDict->GetElement(FX_BSTRC("ActualText"))
-                             : NULL);
+        ToString(pDict ? pDict->GetElement(FX_BSTRC("ActualText")) : nullptr);
     if (temp) {
       actText = temp->GetUnicodeText();
     }