Fix call to CreateFileMappingW.

The call shouldn't rely on the `size` variable, since it is available only
conditionally, based on preprocessor macros.

The `dwMaximumSize{High,Low}` arguments are actually optional, so omitting
them.

https://github.com/yhirose/cpp-httplib/issues/1901

httplib.h

@@ -2859,8 +2859,7 @@ inline bool mmap::open(const char *path) {
   hMapping_ =
       ::CreateFileMappingFromApp(hFile_, NULL, PAGE_READONLY, size_, NULL);
 #else
-  hMapping_ = ::CreateFileMappingW(hFile_, NULL, PAGE_READONLY, size.HighPart,
-                                   size.LowPart, NULL);
+  hMapping_ = ::CreateFileMappingW(hFile_, NULL, PAGE_READONLY, 0, 0, NULL);
 #endif
 
   if (hMapping_ == NULL) {