ArduinoOTA: don't crash on unrecognized packets (esp8266#4086)

* ArduinoOTA: handle end of packet in readStringUntil

fixes esp8266#3912

* ArduinoOTA: fix buffer overflow in parseInt

fixes esp8266#3912

Author: yoursunny

libraries/ArduinoOTA/ArduinoOTA.cpp

@@ -143,10 +143,10 @@ void ArduinoOTAClass::begin() {
 
 int ArduinoOTAClass::parseInt(){
   char data[16];
-  uint8_t index = 0;
+  uint8_t index;
   char value;
   while(_udp_ota->peek() == ' ') _udp_ota->read();
-  while(true){
+  for(index = 0; index < sizeof(data); ++index){
     value = _udp_ota->peek();
     if(value < '0' || value > '9'){
       data[index++] = '\0';
@@ -159,13 +159,13 @@ int ArduinoOTAClass::parseInt(){
 
 String ArduinoOTAClass::readStringUntil(char end){
   String res = "";
-  char value;
+  int value;
   while(true){
     value = _udp_ota->read();
-    if(value == '\0' || value == end){
+    if(value < 0 || value == '\0' || value == end){
       return res;
     }
-    res += value;
+    res += static_cast<char>(value);
   }
   return res;
 }