Fix String::replace()

Fixes: espressif#4920

Author: me-no-dev

cores/esp32/WString.cpp

@@ -744,16 +744,18 @@ void String::replace(const String& find, const String& replace){
  }
  } elseif(diff < 0){
 char *writeTo = wbuffer();
+unsignedint l = len();
 while((foundAt = strstr(readFrom, find.buffer())) != NULL){
 unsignedint n = foundAt - readFrom;
 memmove(writeTo, readFrom, n);
  writeTo += n;
 memmove(writeTo, replace.buffer(), replace.len());
  writeTo += replace.len();
  readFrom = foundAt + find.len();
-setLen(len() + diff);
+l += diff;
  }
 memmove(writeTo, readFrom, strlen(readFrom)+1);
+setLen(l);
  } else{
 unsignedint size = len(); // compute size needed for result
 while((foundAt = strstr(readFrom, find.buffer())) != NULL){
@@ -768,7 +770,7 @@ void String::replace(const String& find, const String& replace){
 while(index >= 0 && (index = lastIndexOf(find, index)) >= 0){
  readFrom = wbuffer() + index + find.len();
 memmove(readFrom + diff, readFrom, len() - (readFrom - buffer()));
-int newLen = len() + diff;
+int newLen = len() + diff;
 memmove(wbuffer() + index, replace.buffer(), replace.len());
 setLen(newLen);
 wbuffer()[newLen] = 0;