rework StreamString::write to use String internal buffer direct.

esp8266#1289

Author: Links2004

cores/esp8266/StreamString.cpp

@@ -23,12 +23,14 @@
 #include <Arduino.h>
 #include "StreamString.h"
 
-size_t StreamString::write(const uint8_t *buffer, size_t size) {
-    if(reserve(length() + size + 1)) {
-        const uint8_t *s = buffer;
-        const uint8_t *end = buffer + size;
-        while(write(*s++) && s < end);
-        return s - buffer;
+size_t StreamString::write(const uint8_t *data, size_t size) {
+    if(size && data) {
+        if(reserve(length() + size + 1)) {
+            memcpy((void *) (buffer + len), (const void *) data, size);
+            len += size;
+            *(buffer + len) = 0x00; // add null for string end
+            return size;
+        }
     }
     return 0;
 }