Windows: Fix bug in shell script shebang lookup code that caused a "delayed read on closed handle" error.

The bug was that withFile closes the handle afterwards, but the content
of the file was not read due to laziness. Using readFile avoids it.

This commit was sponsored by Nick Daly on Patreon.

Utility/Shell.hs

@@ -49,8 +49,7 @@ findShellCommand f = do
 #ifndef mingw32_HOST_OS
 	defcmd
 #else
-	l <- catchDefaultIO Nothing $ withFile f ReadMode $
-		headMaybe . lines <$$> hGetContents
+	l <- catchDefaultIO Nothing $ headMaybe . lines <$> readFile f
 	case l of
 		Just ('#':'!':rest) -> case words rest of
 			[] -> defcmd