g_strdup(NULL) returns NULL; simplify

Signed-off-by: Markus Armbruster <armbru@redhat.com>
Reviewed-by: Eric Blake <eblake@redhat.com>
Signed-off-by: Stefan Hajnoczi <stefanha@redhat.com>
diff --git a/slirp/slirp.c b/slirp/slirp.c
index e93b578..0e6e232 100644
--- a/slirp/slirp.c
+++ b/slirp/slirp.c
@@ -225,12 +225,8 @@
         pstrcpy(slirp->client_hostname, sizeof(slirp->client_hostname),
                 vhostname);
     }
-    if (tftp_path) {
-        slirp->tftp_prefix = g_strdup(tftp_path);
-    }
-    if (bootfile) {
-        slirp->bootp_filename = g_strdup(bootfile);
-    }
+    slirp->tftp_prefix = g_strdup(tftp_path);
+    slirp->bootp_filename = g_strdup(bootfile);
     slirp->vdhcp_startaddr = vdhcp_start;
     slirp->vnameserver_addr = vnameserver;