App UI - messageboxes - notify on incorrect extension

[user0]

XnViewMP 1.6.5 64bit
Windows11 (23H2), display resolution 3840x2160, win scaling 150%

App UI - messageboxes
there is no any indication that opened image has incorrect extension, eg attached GIF image has PNG extension

test_img_gif_with_png_ext.zip

Suggestion

• add new messagebox to
  - notifying user that file extension does not match file signature AND
  - offer to rename file extension

Example

• IrfanView
  msg_rename_extension_irfanview.png

Related

• suggestions
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