Fix const correctness of _sourceValid (#100)

src/AsyncEventSource.h

@@ -82,7 +82,7 @@ class AsyncEventSourceResponse: public AsyncWebServerResponse {
     AsyncEventSourceResponse(AsyncEventSource *server);
     void _respond(AsyncWebServerRequest *request);
     size_t _ack(AsyncWebServerRequest *request, size_t len, uint32_t time);
-    bool _sourceValid(){ return true; }
+    bool _sourceValid() const { return true; }
 };
 
 

src/AsyncJson.h

@@ -65,7 +65,7 @@ class AsyncJsonResponse: public AsyncAbstractResponse {
     }
     ~AsyncJsonResponse() {}
     JsonVariant & getRoot() { return _root; }
-    bool _sourceValid() { return _isValid; }
+    bool _sourceValid() const { return _isValid; }
     size_t setLength() {
       _contentLength = _root.measureLength();
       if (_contentLength) { _isValid = true; }

src/AsyncWebSocket.cpp

@@ -154,7 +154,7 @@ class AsyncWebSocketControl {
       if(_data != NULL)
         free(_data);
     }
-    virtual bool finished(){ return _finished; }
+    virtual bool finished() const { return _finished; }
     uint8_t opcode(){ return _opcode; }
     uint8_t len(){ return _len + 2; }
     size_t send(AsyncClient *client){

src/AsyncWebSocket.h

@@ -219,7 +219,7 @@ class AsyncWebSocketResponse: public AsyncWebServerResponse {
     AsyncWebSocketResponse(const String& key, AsyncWebSocket *server);
     void _respond(AsyncWebServerRequest *request);
     size_t _ack(AsyncWebServerRequest *request, size_t len, uint32_t time);
-    bool _sourceValid(){ return true; }
+    bool _sourceValid() const { return true; }
 };