[basic.compound] Add comma to run-on sentence

Author: eisenwave

source/basic.tex

@@ -5499,7 +5499,7 @@
 a pointer past the end of the last element of
 an array \tcode{x} of $n$ elements
 is considered to be equivalent to
-a pointer to a hypothetical array element $n$ of \tcode{x} and
+a pointer to a hypothetical array element $n$ of \tcode{x}, and
 an object of type \tcode{T} that is not an array element
 is considered to belong to an array with one element of type \tcode{T}.
 The value representation of