Merge pull request #418 from agnat/fix_get_file_size_bug

[Bugfix] Actually invoke the user-supplied function instead of subtracting from a pointer...
diff --git a/tiny_gltf.h b/tiny_gltf.h
index 76ebbfb..0f69ad2 100644
--- a/tiny_gltf.h
+++ b/tiny_gltf.h
@@ -2425,7 +2425,7 @@
 
     size_t file_size{0};
     std::string _err;
-    bool ok = fs-GetFileSizeInBytes(&file_size, &_err, filepath, fs->user_data);
+    bool ok = fs->GetFileSizeInBytes(&file_size, &_err, filepath, fs->user_data);
     if (!ok) {
       if (_err.size()) {
         if (failMsgOut) {