Fix minor GCC10 static analyzer warnings (#7255)

Add minor NULL and double-free checks to source, identified using GCC10
pre-release static `-fanalyzer` on the coude.  These are harmless to
other versions.

Also add explicit include of stdint to Schedule.h, because libstdc++20
will not automatically include it.  Safe and no-op on earlier versions.

Author: earlephilhower

Diff for: cores/esp8266/Schedule.h

@@ -2,6 +2,7 @@
 #define ESP_SCHEDULE_H
 
 #include <functional>
+#include <stdint.h>
 
 #define SCHEDULED_FN_MAX_COUNT 32
 

Diff for: libraries/ESP8266WiFi/src/BearSSLHelpers.cpp

@@ -234,6 +234,8 @@ namespace brssl {
     if (po) {
       free(po->name);
       free(po->data);
+      po->name = nullptr;
+      po->data = nullptr;
     }
   }
 

Diff for: libraries/ESP8266WiFi/src/WiFiClientSecureAxTLS.cpp

@@ -125,6 +125,9 @@ int WiFiClientSecure::_connectSSL(const char* hostName)
 {
     if (!_ssl) {
         _ssl = std::make_shared<SSLContext>();
+	if (!_ssl) {
+          return 0;
+        }
     }
     _ssl->connect(_client, hostName, _timeout);
 
@@ -170,8 +173,7 @@ size_t WiFiClientSecure::write(Stream& stream)
     size_t totalSent = 0;
     size_t countRead;
     size_t countSent;
-    if (!_ssl)
-    {
+    if (!_ssl) {
         return 0;
     }
     do {
@@ -399,61 +401,63 @@ void WiFiClientSecure::_initSSLContext()
 bool WiFiClientSecure::setCACert(const uint8_t* pk, size_t size)
 {
     _initSSLContext();
-    return _ssl->loadObject(SSL_OBJ_X509_CACERT, pk, size);
+    return _ssl ? _ssl->loadObject(SSL_OBJ_X509_CACERT, pk, size) : false;
 }
 
 bool WiFiClientSecure::setCertificate(const uint8_t* pk, size_t size)
 {
     _initSSLContext();
-    return _ssl->loadObject(SSL_OBJ_X509_CERT, pk, size);
+    return _ssl ? _ssl->loadObject(SSL_OBJ_X509_CERT, pk, size) : false;
 }
 
 bool WiFiClientSecure::setPrivateKey(const uint8_t* pk, size_t size)
 {
     _initSSLContext();
-    return _ssl->loadObject(SSL_OBJ_RSA_KEY, pk, size);
+    return _ssl ? _ssl->loadObject(SSL_OBJ_RSA_KEY, pk, size) : false;
 }
 
 bool WiFiClientSecure::setCACert_P(PGM_VOID_P pk, size_t size)
 {
     _initSSLContext();
-    return _ssl->loadObject_P(SSL_OBJ_X509_CACERT, pk, size);
+    return _ssl ? _ssl->loadObject_P(SSL_OBJ_X509_CACERT, pk, size) : false;
 }
 
 bool WiFiClientSecure::setCertificate_P(PGM_VOID_P pk, size_t size)
 {
     _initSSLContext();
-    return _ssl->loadObject_P(SSL_OBJ_X509_CERT, pk, size);
+    return _ssl ? _ssl->loadObject_P(SSL_OBJ_X509_CERT, pk, size) : false;
 }
 
 bool WiFiClientSecure::setPrivateKey_P(PGM_VOID_P pk, size_t size)
 {
     _initSSLContext();
-    return _ssl->loadObject_P(SSL_OBJ_RSA_KEY, pk, size);
+    return _ssl ? _ssl->loadObject_P(SSL_OBJ_RSA_KEY, pk, size) : false;
 }
 
 bool WiFiClientSecure::loadCACert(Stream& stream, size_t size)
 {
     _initSSLContext();
-    return _ssl->loadObject(SSL_OBJ_X509_CACERT, stream, size);
+    return _ssl ? _ssl->loadObject(SSL_OBJ_X509_CACERT, stream, size) : false;
 }
 
 bool WiFiClientSecure::loadCertificate(Stream& stream, size_t size)
 {
     _initSSLContext();
-    return _ssl->loadObject(SSL_OBJ_X509_CERT, stream, size);
+    return _ssl ? _ssl->loadObject(SSL_OBJ_X509_CERT, stream, size) : false;
 }
 
 bool WiFiClientSecure::loadPrivateKey(Stream& stream, size_t size)
 {
     _initSSLContext();
-    return _ssl->loadObject(SSL_OBJ_RSA_KEY, stream, size);
+    return _ssl ? _ssl->loadObject(SSL_OBJ_RSA_KEY, stream, size) : false;
 }
 
 void WiFiClientSecure::allowSelfSignedCerts()
 {
     _initSSLContext();
-    _ssl->allowSelfSignedCerts();
+    if (_ssl) {
+        _ssl->allowSelfSignedCerts();
+    }
 }
 
 extern "C" int __ax_port_read(int fd, uint8_t* buffer, size_t count)