nullable e crash fix

[souzainf3]

Hi, any suggestions to fix crash and swift usage.

1. Add on 'objectWithContentsOfFile' the 'nullable' flag to Swift optional compatibility.
2. Try|catch on 'unarchiveObjectWithData:'.

Bellow the implementation of suggestions.

+ (nullable instancetype)objectWithContentsOfFile:(NSString *)filePath
{
    //load the file
    NSData *data = [NSData dataWithContentsOfFile:filePath];
    
    //attempt to deserialise data as a plist
    id object = nil;
    if (data)
    {
        NSPropertyListFormat format;
        object = [NSPropertyListSerialization propertyListWithData:data options:NSPropertyListImmutable format:&format error:NULL];
       
		//success?
		if (object)
		{
			//check if object is an NSCoded unarchive
			if ([object respondsToSelector:@selector(objectForKeyedSubscript:)] && ((NSDictionary *)object)[@"$archiver"])
			{
                @try {

                    object = [NSKeyedUnarchiver unarchiveObjectWithData:data];
                }
                @catch (NSException* exception) {
                    NSLog(exception);
                    // delete corrupted archive
                    // initialize libraryDat from scratch
                }
			}
		}
		else
		{
			//return raw data
			object = data;
		}
    }
    
	//return object
	return object;
}