When uploading non-binary asset, the mime type is always shown as text/plain making it difficult to know when it is actually stored incorrectly.

The incorrect stored mime type case happens when uploading via zip-upload.

To reproduce (visual issue):

1. upload non image file such as js or csv via upload field
2. Observe resolved mime type (should be correct)
3. save the asset
4. open again for editing
5. Observe resolved mime type (note that this is just a visual error, actual type stored in jcr is correct!)

To reproduce (in repo):

1. pack an image in a zip file
2. zip-upload file with image into dam via Assets app action
3. observe stored mimetype (eg vie JCR Tools/Dumper or via export of the asset)