Fix showOpenWithDialog was rendered outside of viewport on iPads

[ucsbricks]

This pull request makes the fix for the "invisible" open with dialog on iPads originally implemented by @shnist compatible to the new code structure. The user can set the dialog position now. The issue is described in issue #67

[Gillardo]

This change needs to check if the positions are passed in on the ios side not the javascript side. I am using ionic native and because that hasnt been updated , this change crashes the app.

if ([command.arguments count] >= 4) {
        NSArray *positionValues = [command.arguments objectAtIndex:3];
        rect = CGRectMake(0, 0, [[positionValues objectAtIndex:0] floatValue], [[positionValues objectAtIndex:1] floatValue]);
} else {
    rect = CGRectMake(0, 0, cont.view.bounds.size.width, cont.view.bounds.size.height);
}

This is the code i have had to change just to pass in 0, 0 because positionValues doesnt contain any values at all, so it becomes this

if ([command.arguments count] >= 4) {
    NSArray *positionValues = [command.arguments objectAtIndex:3];

        if (![positionValues isEqual:[NSNull null]] && [positionValues count] >= 2) {
                rect = CGRectMake(0, 0, [[positionValues objectAtIndex:0] floatValue], [[positionValues objectAtIndex:1] floatValue]);
        } else {
                rect = CGRectMake(0, 0, 0, 0);
        }
} else {
    rect = CGRectMake(0, 0, cont.view.bounds.size.width, cont.view.bounds.size.height);
}

[Gillardo]

Created a pull request for this https://github.com/pwlin/cordova-plugin-file-opener2/pull/299