allow 'an NPC' from glossary without 'an Non'

glossary.tex

@@ -332,7 +332,8 @@
 
 \newacronym[
   description={ -- anyone in the world played by the \glsentrytext{gm} rather than a player},
-  prefix={a\space},
+  prefix={an\space},
+  prefixfirst={a\space},
   ]{npc}{NPC}{Non-Player Character}
 
 \newglossaryentry{weight}{