[esp32_ble_server] Fix incorrect BLECharacteristic read truncation (#16420) (#16422)

Co-authored-by: Dave <dave@morty>
Co-authored-by: pre-commit-ci-lite[bot] <117423508+pre-commit-ci-lite[bot]@users.noreply.github.com>

esphome/components/esp32_ble_server/ble_characteristic.cpp

@@ -218,13 +218,14 @@ void BLECharacteristic::gatts_event_handler(esp_gatts_cb_event_t event, esp_gatt
         }
       } else {
         response.attr_value.offset = 0;
-        if (this->value_.size() + 1 > max_offset) {
-          response.attr_value.len = max_offset;
-          this->value_read_offset_ = max_offset;
-        } else {
-          response.attr_value.len = this->value_.size();
+        response.attr_value.len = this->value_.size();
+        if (response.attr_value.len > ESP_GATT_MAX_ATTR_LEN) {
+          ESP_LOGW(TAG, "Characteristic length %u exceeds buffer size of %u, truncating", response.attr_value.len,
+                   ESP_GATT_MAX_ATTR_LEN);
+          response.attr_value.len = ESP_GATT_MAX_ATTR_LEN;
         }
         memcpy(response.attr_value.value, this->value_.data(), response.attr_value.len);
+        this->value_read_offset_ = 0;
       }
 
       response.attr_value.handle = this->handle_;