Plugin Directory: Plugin names are being grabbed from the wrong file

[Ipstenu]

When you submit a plugin, it is SUPPOSED to scan the main plugin file for headers, and use that to generate the plugin slug and display name.

That scan should limit itself to the first folder, as otherwise it grabs the wrong data. Like if you've included a sub-plugin with headers it may grab those instead of yours.

[SergeyBiryukov]

In 6026:

Plugin Directory: When searching for the main plugin file on upload, limit recursion depth to 1 level.

Scanning the deeper levels can grab the wrong data, e.g. if there's a sub-plugin with headers, it may be scanned instead of the main one.

Fixes #2804.