Make down-conversion explicit from CFX_ByteString to CFX_ByteStringC.

core/fxcrt/fxcrt_posix.cpp

Index: core/fxcrt/fxcrt_posix.cpp
diff --git a/core/fxcrt/fxcrt_posix.cpp b/core/fxcrt/fxcrt_posix.cpp
index 2f17e71567c70dea87bf664e08f367c1b99c1430..0226313934cd0f35243a5874d133029ca7d34fab 100644
--- a/core/fxcrt/fxcrt_posix.cpp
+++ b/core/fxcrt/fxcrt_posix.cpp
@@ -45,7 +45,7 @@ FX_BOOL CFXCRT_FileAccess_Posix::Open(const CFX_ByteStringC& fileName,
 }
 FX_BOOL CFXCRT_FileAccess_Posix::Open(const CFX_WideStringC& fileName,
                                       uint32_t dwMode) {
-  return Open(FX_UTF8Encode(fileName), dwMode);
+  return Open(FX_UTF8Encode(fileName).AsByteStringC(), dwMode);
 }
 void CFXCRT_FileAccess_Posix::Close() {
   if (m_nFD < 0) {