Prepare does not work properly when plugin has only Android native implementaion

[dtopuzov]

If we have a plugin, valid only for android platform:

"nativescript": {
    "platforms": {
      "android": "2.0.0"
    }
  }

tns prepare ios says "acra-telerik-analytics is not supported for ios", but all the content (aar files) are copied to native ios project

Workaround:

Adding ios key:

  "nativescript": {
    "platforms": {
      "android": "2.0.0",
      "ios": "2.0.0"
    }
  },

results in "Successfully prepared plugin acra-telerik-analytics for ios." and no aars in platform/ios

Notes:
https://github.com/NativeScript/acra-telerik-analytics easily reproduce the bug.

[dtopuzov]

Partially fixed -> platform folder is not copied, but platform specific js files are not processed.