Handle stream timeouts properly, for slow HTTP/HTTPS links (#3752)

This patch fixes update timeouts (error #6) on slow HTTP/HTTPS links.

libraries/Update/src/Updater.cpp

@@ -323,6 +323,8 @@ size_t UpdateClass::write(uint8_t *data, size_t len) {
 size_t UpdateClass::writeStream(Stream &data) {
     size_t written = 0;
     size_t toRead = 0;
+    int timeout_failures = 0;
+
     if(hasError() || !isRunning())
         return 0;
 
@@ -344,15 +346,24 @@ size_t UpdateClass::writeStream(Stream &data) {
             bytesToRead = remaining();
         }
 
+        /* 
+        Init read&timeout counters and try to read, if read failed, increase counter,
+        wait 100ms and try to read again. If counter > 300 (30 sec), give up/abort
+        */
+        toRead = 0;
+        timeout_failures = 0;
+        while(!toRead) {
             toRead = data.readBytes(_buffer + _bufferLen,  bytesToRead);
-        if(toRead == 0) { //Timeout
-            delay(100);
-            toRead = data.readBytes(_buffer + _bufferLen, bytesToRead);
-            if(toRead == 0) { //Timeout
+            if(toRead == 0) {
+                timeout_failures++;
+                if (timeout_failures >= 300) {
                     _abort(UPDATE_ERROR_STREAM);
                     return written;
                 }
+                delay(100);
+            }
         }
+
         if(_ledPin != -1) {
             digitalWrite(_ledPin, !_ledOn); // Switch LED off
         }