[peek, explorer] Update QOI reader for 3-channel images (#39304)

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fix/what does it change/how was it tested (even manually, if necessary)?
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## Summary of the Pull Request

Make sure we account for Bitmap row length being a multiple of 4 when
reading Qoi files.

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## PR Checklist

- [x] **Closes:** #31948
- [ ] **Communication:** Not discussed, but a bug fix
- [ ] **Tests:** Added/updated and all pass
- [ ] **Localization:** All end user facing strings can be localized
- [ ] **Dev docs:** Added/updated
- [ ] **New binaries:** Added on the required places
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## Detailed Description of the Pull Request / Additional comments



<!-- Describe how you validated the behavior. Add automated tests
wherever possible, but list manual validation steps taken as well -->
## Validation Steps Performed

Built and run and restarted file explorer.
Sample files from my comment on the issue (after rewriting each one to
force the thumbnail to regenrate):

![image](https://github.com/user-attachments/assets/5874f958-0f03-4683-abe3-d54c979ad2a1)

Author: mbartlett21

src/common/FilePreviewCommon/QoiImage.cs

@@ -92,6 +92,9 @@ public static Bitmap FromStream(Stream stream)
                 var run = 0;
                 var chunksLen = fileSize - QOI_PADDING_LENGTH;
 
+                var x = 0;
+                var rowAdd = bitmapData.Stride - (channels * bitmapData.Width);
+
                 for (var dataIndex = 0; dataIndex < dataLength; dataIndex += channels)
                 {
                     if (run > 0)
@@ -153,6 +156,14 @@ public static Bitmap FromStream(Stream stream)
                             bitmapPixel[3] = pixel.A;
                         }
                     }
+
+                    x++;
+                    if (x == bitmapData.Width)
+                    {
+                        // We align dataIndex with the stride
+                        dataIndex += rowAdd;
+                        x = 0;
+                    }
                 }
 
                 bitmap.UnlockBits(bitmapData);