res_rtp_asterisk.c: Add conditional module dependency to res_pjproject

* The dependency ensures that res_pjproject cannot be manually unloaded
before res_rtp_asterisk.
* The dependency allows startup loading errors to report that
res_rtp_asterisk depends upon res_pjproject.

Change-Id: Icf5e7581f4ddd6189929f6174c74dd951f887377

res/res_rtp_asterisk.c

@@ -8330,4 +8330,7 @@ AST_MODULE_INFO(ASTERISK_GPL_KEY, AST_MODFLAG_LOAD_ORDER, "Asterisk RTP Stack",
 	.unload = unload_module,
 	.reload = reload_module,
 	.load_pri = AST_MODPRI_CHANNEL_DEPEND,
+#ifdef HAVE_PJPROJECT
+	.requires = "res_pjproject",
+#endif
 );