fix(appium): error when saving screenshot

Author: kobenguyent

lib/helper/WebDriver.js

@@ -1800,6 +1800,13 @@ class WebDriver extends Helper {
 
     const originalWindowSize = await this.browser.getWindowSize()
 
+    // this case running on device, so we could not set the windowSize
+    if (this.browser.isMobile) {
+      this.debug(`Screenshot has been saved to ${outputFile}, size: ${originalWindowSize.width}x${originalWindowSize.height}`)
+      const buffer = await this.browser.saveScreenshot(outputFile)
+      return buffer
+    }
+
     let { width, height } = await this.browser
       .execute(function () {
         return {