__fish_complete_man.fish: escape for regex

Previously, using special regex characters or slashes would result in an
error message, when pressing tab in a command-line such as
"man /usr/bin/time ".

share/functions/__fish_complete_man.fish

@@ -10,7 +10,8 @@ function __fish_complete_man
             case '-**'
 
             case '*'
-                set section $prev[1]
+                set section (string escape --style=regex $prev[1])
+                set section (string replace --all / \\/ $section)
         end
         set -e prev[1]
     end