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### Issue Details
webContents.fromId() for non existing id (e.g. removed webview) causes segmentation fault in Electron 11.
In Electron 9 & 10 null was returned.
Same problem on Windows and macOS Catalina 

* **Electron Version:**
  * 11.0.1
* **Operating System:**
  * macOS 11.0.1
* **Last Known Working Electron version:**
  * 10.1.6

### Expected Behavior
<!-- A clear and concise description of what you expected to happen. -->
webContents.fromId() returns null for non existing id

### Actual Behavior
<!-- A clear and concise description of what actually happened. -->
Segmentation fault

### To Reproduce
https://gist.github.com/larssvensby/071353ec109c4975fd28b5a4b1dc7ad5

### Screenshots
<!-- If applicable, add screenshots to help explain your problem. -->

### Additional Information
<!-- Add any other context about the problem here. -->

shell/browser/api/electron_api_web_contents.cc
options.Get("copies", &copies);
  settings.SetIntKey(printing::kSettingCopies, copies);
   Strings to be printed as headers and footers if requested by the user.
  std::string header;
  options.Get("header", &header);
  std::string footer;
  options.Get("footer", &footer);
  if (!(header.empty() && footer.empty())) {
    settings.SetBoolKey(printing::kSettingHeaderFooterEnabled, true);
    settings.SetStringKey(printing::kSettingHeaderFooterTitle, header);
    settings.SetStringKey(printing::kSettingHeaderFooterURL, footer);
  } else {
    settings.SetBoolKey(printing::kSettingHeaderFooterEnabled, false);
  }
   We don't want to allow the user to enable these settings
   but we need to set them or a CHECK is hit.
  settings.SetIntKey(printing::kSettingPrinterType,
                     static_cast<int>(printing::PrinterType::kLocal));
  settings.SetBoolKey(printing::kSettingShouldPrintSelectionOnly, false);
  settings.SetBoolKey(printing::kSettingRasterizePdf, false);
   Set custom page ranges to print
  std::vector<gin_helper::Dictionary> page_ranges;
  if (options.Get("pageRanges", &page_ranges)) {
    base::Value page_range_list(base::Value::Type::LIST);
    for (auto& range : page_ranges) {
      int from, to;
      if (range.Get("from", &from) && range.Get("to", &to)) {
        base::Value range(base::Value::Type::DICTIONARY);
         Chromium uses 1-based page ranges, so increment each by 1.
        range.SetIntKey(printing::kSettingPageRangeFrom, from + 1);