[dcl.init.general] Insert comma before "or array thereof".

The comma improves the clarity of the binding of "or array thereof",
and was shown in P2996R13, but apparently mistakenly so; it did not
exist in the prior wording. But it is clearly important.

Author: tkoeppe

source/declarations.tex

@@ -5120,9 +5120,10 @@
 \end{itemize}
 
 If a program calls for the default-initialization of an object of a
-const-qualified type \tcode{T}, \tcode{T} shall be
-\tcode{std::meta::\linebreak info} or a const-default-constructible class type or
-array thereof.
+const-qualified type \tcode{T},
+\tcode{T} shall be \tcode{std::meta::\linebreak info}
+or a const-default-constructible class type,
+or array thereof.
 
 \pnum
 To