Update to ESP8266HTTPClient.cpp for no Content-Length (esp8266#7691)

Response bodies are ignored when _transferEncoding == HTTPC_TE_IDENTITY and there is no Content-Length header.  The added code here fixes that issue.

Add logic to writeToStreamDataBlock to only read what's available so as to avoid timeout, and adjust formatting.

Author: drderiv

libraries/ESP8266HTTPClient/src/ESP8266HTTPClient.cpp

@@ -725,7 +725,7 @@ int HTTPClient::writeToStream(Stream * stream)
     int ret = 0;
 
     if(_transferEncoding == HTTPC_TE_IDENTITY) {
-        if(len > 0) {
+        if(len > 0 || len == -1) {
             ret = writeToStreamDataBlock(stream, len);
 
             // have we an error?
@@ -1184,6 +1184,12 @@ int HTTPClient::writeToStreamDataBlock(Stream * stream, int size)
         if(readBytes > buff_size) {
             readBytes = buff_size;
         }
+    
+        // len == -1 or len > what is available, read only what is available
+        int av = _client->available();
+        if (readBytes < 0 || readBytes > av) {
+            readBytes = av;
+        }
 
         // read data
         int bytesRead = _client->readBytes(buff, readBytes);