32bit exr file has incorrect bitdepth of 16.

[bug.zip](https://github.com/dlemstra/Magick.NET/files/3355302/bug.zip)

### Prerequisites

- [x] I have written a descriptive issue title
- [x] I have verified that I am using the latest version of Magick.NET
- [x] I have searched [open](https://github.com/dlemstra/Magick.NET/issues) and [closed](https://github.com/dlemstra/Magick.NET/issues?q=is%3Aissue+is%3Aclosed) issues to ensure it has not already been reported

### Description
I have a 32bit exr file with values [0-1]. When opened in Photoshop it says 32 bit / channel under Image - Mode.

When loading this image with Magick.NET-Q16-HDRI-AnyCPU the _Depth_ property or _BitDepth_ method both return 16. When I attempt to save this file as a .tif it saves a 16bit tif.

I can save a correct looking 32bit tiff by first setting the depth to 32 and then saving it again.

The ColorType is set to TrueColorAlpha, but when I set it to TrueColorAlpha again the pixel values in the 32bit tiff (or 16bit) have changed. I don't understand why this is happening? I set TrueColorAlpha because otherwise single channel true color images are saved as 8-bit indexed as reported here: https://github.com/dlemstra/Magick.NET/issues/376.

### Steps to Reproduce
```
var image = new MagickImage(@"E:\magick\exr\bug.exr");
image.Depth.Dump(); //16
image.BitDepth().Dump(); //16

var tiffWriteDefines = new TiffWriteDefines { Alpha = TiffAlpha.Unspecified };
image.Write(@"E:\magick\exr\out_bug.tif", tiffWriteDefines); // 16 bit tiff

image.BitDepth(32); // force 32bit
image.Write(@"E:\magick\exr\out_bug_force_32.tif", tiffWriteDefines); // 32 bit tiff
```

ColorType issues:
```
// I would imagine this has no effect... but it does.
if (image.ColorType == ColorType.TrueColorAlpha)
{
image.ColorType = ColorType.TrueColorAlpha;
}

image.Write(@"E:\magick\exr\out_bug_color_type.tif", tiffWriteDefines); // looks different.
```

### System Configuration
- Magick.NET version: 7.14.0.2
- Environment (Operating system, version and so on): Windows 10
- Additional information: