Fail zlib-decompress-region if loading zlib on Windows failed.

 src/decompress.c (Fzlib_decompress_region) [WINDOWSNT]: Return Qnil
 if loading zlib failed.

src/ChangeLog

+2013-08-13  Eli Zaretskii  <eliz@gnu.org>
+
+	* decompress.c (Fzlib_decompress_region) [WINDOWSNT]: Return Qnil
+	if loading zlib failed.
+
 2013-08-13  Jan Djärv  <jan.h.d@swipnet.se>
 
 	* nsterm.m (ns_set_vertical_scroll_bar): Fix breakage intruduced by

src/decompress.c

@@ -146,6 +146,8 @@ This function can be called only in unibyte buffers.  */)
 #ifdef WINDOWSNT
   if (!zlib_initialized)
     zlib_initialized = init_zlib_functions ();
+  if (!zlib_initialized)
+    return Qnil;
 #endif
 
   /* This is a unibyte buffer, so character positions and bytes are