Fix possible null dereferences.

src/loop.c

@@ -498,10 +498,11 @@ int mosquitto_main_loop(struct mosquitto_db *db, mosq_sock_t *listensock, int li
 								}
 								context = NULL;
 								HASH_FIND(hh_sock, db->contexts_by_sock, &(ev.data.fd), sizeof(mosq_sock_t), context);
-								if(!context) {
+								if(context){
+									context->events = EPOLLIN;
+								}else{
 									log__printf(NULL, MOSQ_LOG_ERR, "Error in epoll accepting: no context");
 								}
-								context->events = EPOLLIN;
 							}
 						}
 						break;

src/subs.c

@@ -216,8 +216,8 @@ static struct sub__token *sub__topic_append(struct sub__token **tail, struct sub
 static int sub__topic_tokenise(const char *subtopic, struct sub__token **topics)
 {
 	struct sub__token *new_topic, *tail = NULL;
-	int len;
-	int start, stop, tlen;
+	size_t len;
+	size_t start, stop, tlen;
 	int i;
 	char *topic;
 	int count = 0;
@@ -225,13 +225,16 @@ static int sub__topic_tokenise(const char *subtopic, struct sub__token **topics)
 	assert(subtopic);
 	assert(topics);
 
+	len = strlen(subtopic);
+	if(len == 0){
+		return 1;
+	}
+
 	if(subtopic[0] != '$'){
 		new_topic = sub__topic_append(&tail, topics, "");
 		if(!new_topic) goto cleanup;
 	}
 
-	len = strlen(subtopic);
-
 	if(subtopic[0] == '/'){
 		new_topic = sub__topic_append(&tail, topics, "");
 		if(!new_topic) goto cleanup;
@@ -268,7 +271,11 @@ static int sub__topic_tokenise(const char *subtopic, struct sub__token **topics)
 		goto cleanup;
 	}
 
-	return MOSQ_ERR_SUCCESS;
+	if(*topics != NULL){
+		return MOSQ_ERR_SUCCESS;
+	}else{
+		return 1;
+	}
 
 cleanup:
 	tail = *topics;