Fix adding of invalid platform

When user tries to add invalid platform, CLI should prints user-friendly
message. Instead it fails that cannot read `getPlatformData` of
`undefined`. The reason is a change in platforms-data `getPlatformsData`
method. Fix it to return undefined when there's no platform specific
data. This way the code will detect the invalid platform and will fail
with user-friendly message.

Author: rosen-vladimirov

lib/platforms-data.ts

@@ -15,7 +15,7 @@ export class PlatformsData implements IPlatformsData {
 	}
 
 	public getPlatformData(platform: string, projectData: IProjectData): IPlatformData {
-		return this.platformsData[platform.toLowerCase()].getPlatformData(projectData);
+		return this.platformsData[platform.toLowerCase()] && this.platformsData[platform.toLowerCase()].getPlatformData(projectData);
 	}
 
 	public get availablePlatforms(): any {