#3181 printf double vsnprintf() fix, malloc, va_end (#3184)

* Use loc_buf for small strings, check for error return from vsnprintf

* cleanup arg when bailing out of new

* Use malloc/free instead of new/delete in printf

* Return actual bytes written in printf

* FIX: write before free

cores/esp32/Print.cpp

@@ -52,19 +52,24 @@ size_t Print::printf(const char *format, ...)
     va_list copy;
     va_start(arg, format);
     va_copy(copy, arg);
-    size_t len = vsnprintf(NULL, 0, format, copy);
+    int len = vsnprintf(temp, sizeof(loc_buf), format, copy);
     va_end(copy);
+    if(len < 0) {
+        va_end(arg);
+        return 0;
+    };
     if(len >= sizeof(loc_buf)){
-        temp = new char[len+1];
+        temp = (char*) malloc(len+1);
         if(temp == NULL) {
+            va_end(arg);
             return 0;
         }
+        len = vsnprintf(temp, len+1, format, arg);
     }
-    len = vsnprintf(temp, len+1, format, arg);
-    write((uint8_t*)temp, len);
     va_end(arg);
-    if(len >= sizeof(loc_buf)){
-        delete[] temp;
+    len = write((uint8_t*)temp, len);
+    if(temp != loc_buf){
+        free(temp);
     }
     return len;
 }