Aperio AppMag parsing int vs double.

[Leonardo Romor]

Dear Openslide developers,

Regarding the Aperio format, we noticed some edge cases that do not allow
the current openslide aperio implementation to parse correctly the AppMag
of the WSI.

An example image is provided at this link:
https://portal.gdc.cancer.gov/files/1fd8ba85-547b-435f-830e-a436746990fd

Using tiffinfo you can see that:

95744x86336 (256x256) J2K/KDU Q=70;Leica SCN400;Leica SCN
ver.1.5.1.10804 2012/05/10 13:29:07;1.5.1.10864|Filename =
ImageCollection_0000000935|Date = 2014-07-23T16:33:58.37Z|AppMag =
40.000000|MPP = 0.250000|OriginalWidth = 86336|OriginalHeight = 95744

As you can see, the AppMag metadata is represented as a float value instead
as of an int (|AppMag = 40|) . This leads to an unparsed AppMag. We propose
to change "_openslide_duplicate_int_prop" into
"_openslide_duplicate_double_prop" or allow the int version to parse and
then cast float values in the following line of code:

https://github.com/openslide/openslide/blob/c3391de109f736e8164bec27176e42bacae462a5/src/openslide-vendor-aperio.c#L327

Would it be possible for you to solve this issue or do you accept
pull-requests?

Best regards,

Leonardo Romor

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