Guard against no devtools web contents

lib/browser/api/browser-window.js

@@ -138,14 +138,17 @@ BrowserWindow.getFocusedWindow = () => {
 }
 
 BrowserWindow.fromWebContents = (webContents) => {
-  for (let window of BrowserWindow.getAllWindows()) {
+  for (const window of BrowserWindow.getAllWindows()) {
     if (window.webContents.equal(webContents)) return window
   }
 }
 
 BrowserWindow.fromDevToolsWebContents = (webContents) => {
-  for (let window of BrowserWindow.getAllWindows()) {
-    if (window.devToolsWebContents.equal(webContents)) return window
+  for (const window of BrowserWindow.getAllWindows()) {
+    const {devToolsWebContents} = window
+    if (devToolsWebContents != null && devToolsWebContents.equal(webContents)) {
+      return window
+    }
   }
 }