[expr.dynamic.cast] Add comma after conditional clause (#6830)

Author: Eisenwave

source/expressions.tex

@@ -3827,7 +3827,8 @@
 \item If, in the most derived object pointed (referred) to by \tcode{v},
 \tcode{v} points (refers) to a public base class subobject of a
 \tcode{C} object, and if only one object of type \tcode{C} is derived
-from the subobject pointed (referred) to by \tcode{v} the result points (refers) to that \tcode{C} object.
+from the subobject pointed (referred) to by \tcode{v},
+the result points (refers) to that \tcode{C} object.
 
 \item Otherwise, if \tcode{v} points (refers) to a public base
 class subobject of the most derived object, and the type of the most