CB-13571: (android) Prevent crash with unrecognized android version

Fixes issue where commands that list images will crash when an image with a version not present in `android-versions` is encountered, as is presently the case with API 27:

```
cordova run android --list
Available android devices:
Available android virtual devices:
LEVEL: null
ERROR: TypeError: Cannot read property 'semver' of null
An unexpected error has occured while running list-emulator-images with code 2: Error: /home/chris/Repositories/acp-guidelines/cordova/platforms/android/cordova/lib/list-emulator-images: Command failed with exit code 2
```

Signed-off-by: Chris Alfano <chris@jarv.us>

bin/templates/cordova/lib/emulator.js

@@ -187,7 +187,9 @@ module.exports.list_images = function () {
                 var api_level = avd.target.match(/\d+/);
                 if (api_level) {
                     var level = android_versions.get(api_level);
-                    avd.target = 'Android ' + level.semver + ' (API level ' + api_level + ')';
+                    if (level) {
+                        avd.target = 'Android ' + level.semver + ' (API level ' + api_level + ')';
+                    }
                 }
             }
             return avd;