Fix String::clear() not clearing the string properly

Fixes: espressif#4893

Author: me-no-dev

cores/esp32/WString.cpp

@@ -130,9 +130,9 @@ String::~String() {
 
 inline void String::init(void) {
  setSSO(false);
+ setBuffer(nullptr);
  setCapacity(0);
  setLen(0);
- setBuffer(nullptr);
 }
 
 void String::invalidate(void) {

cores/esp32/WString.h

@@ -301,9 +301,19 @@ class String {
  inline unsigned int len() const { return isSSO() ? sso.len : ptr.len; }
  inline unsigned int capacity() const { return isSSO() ? (unsigned int)SSOSIZE - 1 : ptr.cap; } // Size of max string not including terminal NUL
  inline void setSSO(bool set) { sso.isSSO = set; }
- inline void setLen(int len) { if (isSSO()) sso.len = len; else ptr.len = len; }
+ inline void setLen(int len) {
+ if (isSSO()) {
+ sso.len = len;
+ sso.buff[len] = 0;
+ } else {
+ ptr.len = len;
+ if (ptr.buff) {
+ ptr.buff[len] = 0;
+ }
+ }
+ }
  inline void setCapacity(int cap) { if (!isSSO()) ptr.cap = cap; }
-inline void setBuffer(char *buff) { if (!isSSO()) ptr.buff = buff; }
+ inline void setBuffer(char *buff) { if (!isSSO()) ptr.buff = buff; }
  // Buffer accessor functions
  inline const char *buffer() const { return (const char *)(isSSO() ? sso.buff : ptr.buff); }
  inline char *wbuffer() const { return isSSO() ? const_cast<char *>(sso.buff) : ptr.buff; } // Writable version of buffer