Make CFX_WideString(const CFX_WideString&) explicit.

core/fpdfdoc/doc_basic.cpp

Index: core/fpdfdoc/doc_basic.cpp
diff --git a/core/fpdfdoc/doc_basic.cpp b/core/fpdfdoc/doc_basic.cpp
index a0c6b2babc4494562af14b35178778dbebb6c01b..76639efac66743f6a9fbe0942543f32f1cd2941f 100644
--- a/core/fpdfdoc/doc_basic.cpp
+++ b/core/fpdfdoc/doc_basic.cpp
@@ -315,7 +315,7 @@ CFX_WideString CPDF_FileSpec::DecodeFileName(const CFX_WideStringC& filepath) {
   result += ChangeSlashToPlatform(filepath.c_str());
   return result;
 #else
-  return filepath;
+  return CFX_WideString(filepath);
 #endif
 }
 
@@ -390,7 +390,7 @@ CFX_WideString CPDF_FileSpec::EncodeFileName(const CFX_WideStringC& filepath) {
   }
   return ChangeSlashToPDF(filepath.c_str());
 #else
-  return filepath;
+  return CFX_WideString(filepath);
 #endif
 }