ESP32 SDCard reinitialize issue

[alberk8]

Details about Problem

When SDCard is disposed subsequent reinitialization will fail.

Target:
ESP32 WROVER

Firmware image version:
1.7.1-preview.1125

Worked before? If so, with which nanoFramework image version:
Not sure.

Description

An exception is thrown when subsequent attempt to reinitialized the SDCard class.

Detailed repro steps so we can see the same problem

 var mycard = new SDCard(new SDCard.SDCardMmcParameters { dataWidth = SDCard.SDDataWidth._4_bit });
 mycard.Mount();
 mycard.Unmount();
 mycard.Dispose();

// fail here
var mycard1 = new SDCard(new SDCard.SDCardMmcParameters { dataWidth = SDCard.SDDataWidth._4_bit });
 mycard1.Mount();
 mycard1.Unmount();
 mycard1.Dispose();

Other suggested things

Exception Thrown

++++ Exception System.Exception - CLR_E_PIN_UNAVAILABLE (1) ++++
++++ Message: 
++++ nanoFramework.System.IO.FileSystem.SDCard::InitNative [IP: 0000] ++++
++++ nanoFramework.System.IO.FileSystem.SDCard::.ctor [IP: 0025] ++++
++++ nanoFrameworkSDCard.Program::Main [IP: 0029] ++++
Exception thrown: 'System.Exception' in System.IO.FileSystem.dll
An unhandled exception of type 'System.Exception' occurred in System.IO.FileSystem.dll

Expected behaviour

SDCard class should not throw exception if it was previously disposed.

[AdrianSoundy]

Looks like a problem removing reserve from SDIO pins.