Problem: When a float window with style='minimal' is converted to a
split window and then changes buffer, the minimal style options get
overridden. This happens because merge_win_config() clears the style
field, so get_winopts() doesn't know to re-apply minimal style after
restoring options from the buffer's wininfo.
Solution: Save and restore the style field when clearing the config
during float-to-split conversion.
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