Move the two low-level file I/O helper to their respective single place of usage.

rtengine/myfile.cc

@@ -68,7 +68,25 @@ int munmap(void *start, size_t length)
 
 IMFILE* fopen (const char* fname)
 {
-    int fd = safe_open_ReadOnly(fname);
+    int fd = -1;
+
+#ifdef WIN32
+
+    {
+        // First convert UTF8 to UTF16, then use Windows function to open the file and convert back to file descriptor.
+        std::unique_ptr<wchar_t, GFreeFunc> wfname (reinterpret_cast<wchar_t*>(g_utf8_to_utf16 (fname, -1, NULL, NULL, NULL)), g_free);
+
+        HANDLE hFile = CreateFileW (wfname.get (), GENERIC_READ, FILE_SHARE_READ, NULL, OPEN_EXISTING, FILE_ATTRIBUTE_NORMAL, NULL);
+        if (hFile != INVALID_HANDLE_VALUE) {
+            fd = _open_osfhandle((intptr_t)hFile, 0);
+        }
+    }
+
+#else
+
+    fd = ::g_open (fname, O_RDONLY);
+
+#endif
 
     if ( fd < 0 ) {
         return 0;