Fixed error in error handling

Summary:
During component cleanup broke the error handling :'). Causing plugin errors to bubble up and be handled as chrome errors instead. This caused our soft crash metric to spike in the last week.

Changelog: Fixed error handling of UI errors caused by plugins

Reviewed By: passy

Differential Revision: D29585448

fbshipit-source-id: 4c5d40b300a7b71eeb532f7be4765f742d239890

desktop/app/src/ui/components/ErrorBoundary.tsx

@@ -79,7 +79,9 @@ export default class ErrorBoundary extends Component<
         <ErrorBoundaryContainer grow>
           <Heading>{heading}</Heading>
           {this.props.showStack !== false && (
-            <ErrorBoundaryStack>{error}</ErrorBoundaryStack>
+            <ErrorBoundaryStack>{`${
+              error.stack ?? error.toString()
+            }`}</ErrorBoundaryStack>
           )}
           <Button onClick={this.clearError}>Clear error and try again</Button>
         </ErrorBoundaryContainer>