Provide a better recovery path after installing an invalid theme

app/src/browser/application.es6

@@ -503,9 +503,24 @@ export default class Application extends EventEmitter {
       }
     });
 
-    ipcMain.on('ensure-worker-window', () => {
-      // TODO BG
-      // this.windowManager.ensureWindow(WindowManager.MAIN_WINDOW)
+    // Theme Error Handling
+
+    let userResetTheme = false;
+
+    ipcMain.on('encountered-theme-error', (event, { message, detail }) => {
+      if (userResetTheme) return;
+
+      const buttonIndex = dialog.showMessageBox({
+        type: 'warning',
+        buttons: ['Reset Theme', 'Continue'],
+        defaultId: 0,
+        message,
+        detail,
+      });
+      if (buttonIndex === 0) {
+        userResetTheme = true;
+        this.config.set('core.theme', '');
+      }
     });
 
     ipcMain.on('inline-style-parse', (event, { html, key }) => {

app/src/theme-manager.es6

@@ -1,3 +1,4 @@
+import { ipcRenderer } from 'electron';
 import { Emitter } from 'event-kit';
 import path from 'path';
 import fs from 'fs-plus';
@@ -202,7 +203,10 @@ export default class ThemeManager {
       }
       console.error(message, { detail, dismissable: true });
       console.error(detail);
-      throw error;
+
+      ipcRenderer.send('encountered-theme-error', { message, detail });
+
+      return '';
     }
   }
 }