func_presencestate: Fix invalid memory access.

When parsing information from AstDB while loading,
it is possible that certain pointers are never
set, which leads to invalid memory access and
then, fatally, invalid free attempts on this memory.
We now initialize to NULL to prevent this.

ASTERISK-30311 #close

Change-Id: I6120681d04fd2c12a9473f35ce95a1f8e74e3929

funcs/func_presencestate.c

@@ -850,8 +850,8 @@ static int load_module(void)
 	for (; db_entry; db_entry = db_entry->next) {
 		const char *dev_name = strrchr(db_entry->key, '/') + 1;
 		enum ast_presence_state state;
-		char *message;
-		char *subtype;
+		char *message = NULL;
+		char *subtype = NULL;
 		if (dev_name <= (const char *) 1) {
 			continue;
 		}