[over.oper] Clarify that the 'has a parameter of class or enum type' constraint

on overloaded operators only applies to the non-member case.

Author: zygoloid

source/overloading.tex

@@ -2876,8 +2876,8 @@
 \pnum
 \indextext{restriction!overloading}%
 An operator function
-shall either be a non-static member function or be a non-member function and
-have at least one parameter whose type is a class, a reference to a class, an
+shall either be a non-static member function or be a non-member function that
+has at least one parameter whose type is a class, a reference to a class, an
 enumeration, or a reference to an enumeration.
 It is not possible to change the precedence, grouping, or number of operands
 of operators.