fish: check for dict and shuf before doing fish_greeting

scripts/fish/prompt

@@ -13,6 +13,7 @@ function fish_right_prompt
 end
 
 function fish_greeting
+	if test -f /usr/share/dict/words && test (what shuf)
 		set_color c50ed2
 
 		echo "Word of the moment: "(shuf -n1 /usr/share/dict/words) |
@@ -20,5 +21,6 @@ function fish_greeting
 
 		set_color normal
 	end
+end
 
 ## EOF