Regression - hs.image:colorAt() doesn't handle scale correctly

[latenitefilms]

The changes made here:

5d34265

...don't seem to take into account the correct scale (because the NSImage size method returns size information that is screen resolution dependent).

@randomeizer has come up with the suggested fix, which I'll do a pull request for shortly:

/// hs.image:colorAt(point) -> table
/// Method
/// Reads the color of the pixel at the specified location.
///
/// Parameters:
///  * `point` - a `hs.geometry.point`
///
/// Returns:
///  * A `hs.drawing.color` object
static int colorAt(lua_State* L) {
    LuaSkin *skin = [LuaSkin sharedWithState:L] ;
    [skin checkArgs:LS_TUSERDATA, USERDATA_TAG, LS_TTABLE, LS_TBREAK];

    NSImage *theImage = [skin luaObjectAtIndex:1 toClass:"NSImage"] ;
    NSPoint point  = [skin tableToPointAtIndex:2] ;

    NSColor *pixelColor = nil;
    @autoreleasepool {
        CGImageRef CGImage = [theImage CGImageForProposedRect:nil context:nil hints:nil];
        NSBitmapImageRep *rep = [[NSBitmapImageRep alloc] initWithCGImage:CGImage];
        NSSize imageSize = [theImage size];
        NSSize bitmapSize = [rep size];
        CGFloat xScale = bitmapSize.width / imageSize.width;
        CGFloat yScale = bitmapSize.height / imageSize.height;
        pixelColor = [rep colorAtX:(point.x * xScale) y:(point.y * yScale)];
    }
    
    [skin pushNSObject:pixelColor];

    return 1;
}