mapi32: Write-strings warnings fix

[Andrew Talbot]

Changelog:
    mapi32: Write-strings warnings fix.

diff -urN a/dlls/mapi32/sendmail.c b/dlls/mapi32/sendmail.c
--- a/dlls/mapi32/sendmail.c	2006-05-23 17:24:40.000000000 +0100
+++ b/dlls/mapi32/sendmail.c	2006-07-03 21:06:27.000000000 +0100
@@ -63,7 +63,8 @@
     unsigned int i, to_count = 0, cc_count = 0, bcc_count = 0;
     unsigned int to_size = 0, cc_size = 0, bcc_size = 0, subj_size, body_size;
 
-    char *address = "", *to = NULL, *cc = NULL, *bcc = NULL, *subject, *body;
+    char *address, *to = NULL, *cc = NULL, *bcc = NULL;
+    const char *subject, *body;
     static const char format[] =
         "mailto:\"%s\"?subject=\"%s\"&cc=\"%s\"&bcc=\"%s\"&body=\"%s\"";
     char *mailto = NULL, *escape = NULL;