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.

CHANGELOG

@@ -15,6 +15,8 @@ git-annex (6.20170301.2) UNRELEASED; urgency=medium
     program, searching for the program in the PATH.
   * Drop support for building with old versions of dns, http-conduit,
     directory, feed, and http-types.
+  * Windows: Fix bug in shell script shebang lookup code that
+    caused a "delayed read on closed handle" error.
 
  -- Joey Hess <id@joeyh.name>  Thu, 02 Mar 2017 12:51:40 -0400
 

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

doc/bugs/external_remote_hGetContents_handle_error.mdwn

@@ -40,3 +40,5 @@ Same as before, windows, git-bash
 ### Have you had any luck using git-annex before? (Sometimes we get tired of reading bug reports all day and a lil' positive end note does wonders)
 
 Thanks for the quick response earlier. I hope this is helpful information. Keep up the great work! :)
+
+> Reproduced this bug, and I've committed a fix. [[done]] --[[Joey]]