Fixed ticket #938: Presence PIDF document may be rejected by presence servers that implement strict XML checking (thanks Johan Lantz for the fix)

git-svn-id: https://svn.pjsip.org/repos/pjproject/trunk@2876 74dad513-b988-da41-8d7b-12977e46ad98
diff --git a/pjsip/src/pjsip-simple/presence_body.c b/pjsip/src/pjsip-simple/presence_body.c
index 8754735..01b4e85 100644
--- a/pjsip/src/pjsip-simple/presence_body.c
+++ b/pjsip/src/pjsip-simple/presence_body.c
@@ -85,6 +85,8 @@
 	/* Add tuple id. */
 	if (status->info[i].id.slen == 0) {
 	    pj_create_unique_string(pool, &id);
+	    /* xs:ID must start with letter */
+	    id.ptr[0] = 'p';
 	} else {
 	    id = status->info[i].id;
 	}