[gmime] Fixed the build on MSVC

[Jeffrey Stedfast <fejj src gnome org>]

commit 44765a11499a43a2d791677d58a88f28fb186b8a
Author: Jeffrey Stedfast <jestedfa microsoft com>
Date:   Thu Nov 30 11:29:47 2017 -0500

    Fixed the build on MSVC
    
    Thanks to Gisle Vanem for finding this bug

 gmime/gmime-autocrypt.c |    2 +-
 1 files changed, 1 insertions(+), 1 deletions(-)
---
diff --git a/gmime/gmime-autocrypt.c b/gmime/gmime-autocrypt.c
index 104c27c..e13b727 100644
--- a/gmime/gmime-autocrypt.c
+++ b/gmime/gmime-autocrypt.c
@@ -449,7 +449,7 @@ g_mime_autocrypt_header_to_string (GMimeAutocryptHeader *ah, gboolean gossip)
        const size_t firstline = maxwid - sizeof ("Autocrypt:");
        gsize offset = 0;
        gsize ksz = 0;
-       gconstpointer kp = g_bytes_get_data (ah->keydata, &ksz);
+       const guchar *kp = g_bytes_get_data (ah->keydata, &ksz);
        if (n < firstline) {
                gsize firstlinekeylen = ((firstline - n)/4)*3;
                if (firstlinekeylen > ksz)