app_minivm: Fix possible uninitialized return value.

Declare 'res' initialized to -1 to deal with earlier error paths that
could cause 'res' to be returned uninitialized.

Change-Id: I8ac2a5755bf4174d89ef893e924c940f702b104e

apps/app_minivm.c

@@ -1254,7 +1254,7 @@ static int sendmail(struct minivm_template *template, struct minivm_account *vmu
 	struct ast_channel *chan = NULL;
 	char *fromaddress;
 	char *fromemail;
-	int res;
+	int res = -1;
 
 	if (!str1 || !str2) {
 		return -1;