iterator::operator== fix for C++20 (#1798)

* fix incorrect C++ standard library usage to make C++20 build work

* [pre-commit.ci] auto fixes from pre-commit.com hooks

for more information, see https://pre-commit.ci

---------

Co-authored-by: pre-commit-ci[bot] <66853113+pre-commit-ci[bot]@users.noreply.github.com>

Author: BenWibking

src/IO/ADIOS/ADIOS2PreloadVariables.cpp

@@ -56,7 +56,8 @@ namespace
         }
         auto operator==(FilteredInputIterator const &other) const -> bool
         {
-            return static_cast<Iterator const *>(this)->operator==(other);
+            return static_cast<Iterator const &>(*this) ==
+                static_cast<Iterator const &>(other);
         }
         using Iterator::operator*;
         using Iterator::operator->;