res_ari: Add "module loaded" check to ari stubs

The recent change to make the use of LOAD_DECLINE more consistent
caused res_ari to unload itself before declining if the ari.conf
file wasn't found.  The ari stubs though still tried to use the
configuration resulting in segfaults.

This patch creates a new CHECK_ARI_MODULE_LOADED macro which tests
to see if res_ari is actually loaded and causes the stubs to also
decline if it isn't.  The macro was then added to the mustache
template's "load_module" function.

ASTERISK-27026 #close
Reported-by: Ronald Raikes

Change-Id: I263d56efa628ee3c411bdcd16d49af6260c6c91d

include/asterisk/ari.h

@@ -268,4 +268,14 @@ void ast_ari_response_created(struct ast_ari_response *response,
  */
 void ast_ari_response_alloc_failed(struct ast_ari_response *response);
 
+/*! \brief Determines whether the res_ari module is loaded */
+#define CHECK_ARI_MODULE_LOADED()				\
+	do {							\
+		if (!ast_module_check("res_ari.so")		\
+			|| !ast_ari_oom_json()) {	\
+			return AST_MODULE_LOAD_DECLINE;		\
+		}						\
+	} while(0)
+
+
 #endif /* _ASTERISK_ARI_H */