[alg.copy] Add missing words.

Those were accidentally omitted in the application of P3179R9.

Author: tkoeppe

source/algorithms.tex

@@ -6593,7 +6593,7 @@
   for the overloads in namespace \tcode{std}.
 \item
   \tcode{\{last, result + $N$\}}
-  for the overloads in namespace \tcode{ranges}.
+  for the overloads in namespace \tcode{ranges}, if $N$ is equal to $M$.
 \item
   Otherwise, \tcode{\{j, result_last\}}
   for the overloads in namespace \tcode{ranges},