[util.smartptr.atomic.shared] [util.smartptr.atomic.weak] Clarify

grouping of "either".

Author: zygoloid

source/utilities.tex

@@ -11851,7 +11851,7 @@
 \remarks
 Two \tcode{shared_ptr} objects are equivalent if
 they store the same pointer value and
-either share ownership, or both are empty.
+either share ownership or are both empty.
 The weak form may fail spuriously. See \ref{atomics.types.operations}.
 
 \pnum
@@ -12090,7 +12090,7 @@
 \remarks
 Two \tcode{weak_ptr} objects are equivalent if
 they store the same pointer value and
-either share ownership, or both are empty.
+either share ownership or are both empty.
 The weak form may fail spuriously. See \ref{atomics.types.operations}.
 
 \pnum