ENH: treat self-assignment as no-op instead of a Fatal (#1473)

- this can help if using std algorithms that return a const reference
  such as std::min() does.

src/OpenFOAM/db/IOobjects/CompactIOField/CompactIOField.C

@@ -215,6 +215,11 @@ void Foam::CompactIOField<T, BaseType>::operator=
     const CompactIOField<T, BaseType>& rhs
 )
 {
+    if (this == &rhs)
+    {
+        return;  // Self-assigment is a no-op
+    }
+
     Field<T>::operator=(rhs);
 }