fix(file_dialog): free of uninitialized enumerator

Author: Tom94

src/common.cpp

@@ -363,8 +363,6 @@ file_dialog(Widget *parent,
     else if (result != NFD_OKAY)
         throw std::runtime_error("nanogui::file_dialog(): dialog error: " + std::string(NFD_GetError()));
 
-    enumerator_set = true;
-
     std::vector<std::string> paths;
 
     switch (type) {
@@ -378,6 +376,7 @@ file_dialog(Widget *parent,
         case FileDialogType::OpenMultiple:
             if (!NFD_PathSet_GetEnum(out_paths, &enumerator))
                 throw std::runtime_error("nanogui::file_dialog(): could not obtain enumerator: " + std::string(NFD_GetError()));
+            enumerator_set = true;
             while (NFD_PathSet_EnumNextU8(&enumerator, &out_path) && out_path)
                 paths.emplace_back(out_path);
             break;