fix json parsing error on upload

[mfkl]

When trying to push a nuget package containing an icon and a readme inside the nupkg (such as libvlcsharp), I'm hitting the following error:

Unexpected character encountered while parsing value: �. Path '', line 0, position 0 

You can reproduce and catch the exception here

Sleet/src/SleetLib/Utility/JsonUtility.cs

Line 178 in 52ac190

var json = await JObject.LoadAsync(jsonReader, _jsonLoadSettings);

readmes and icons are under the form of bc843690-b6b7-44f9-9527-bab8a374809e\07e7da76-8654-4d33-8f2f-aa9dafec230b.tmp for LocalCacheFile.FullName and the current if logic is not detecting them early enough, so I just moved them around.

[emgarten]

Is your icon or readme also json allowing it to pass the check?

This looks like a good fix overall, those files should be checked first before the more generic cases.

[emgarten]

This fix was released in v6.5.10

[mfkl]

Is your icon or readme also json allowing it to pass the check?

No, they are regular png/markdown files, but with the code below, the json check runs (and fails) anyway:

else if (key.EndsWith(".json", StringComparison.Ordinal) || await JsonUtility.IsJsonAsync(LocalCacheFile.FullName))

Thanks for the quick merge.