Make the NDS teardown more robust (#1798)

* Make cleanup a little more robust to mitigate undefined behavior

- Add some null checks before cleaning up the GPU3D renderer
- Make sure that all deleted objects are null
- Move cleanup logic out of an assert call
- Note that deleting a null pointer is a no-op, so there's no need to check for null beforehand
- Use RAII for GLCompositor instead of Init/DeInit methods

* Replace a DeInit call that I missed

* Make ARMJIT_Memory less likely to generate errors

- Set FastMem7/9Start to nullptr at the end
- Only close and unmap the file if it's initialized

* Make Renderer3D manage its resources with RAII

* Don't try to deallocate frontend resources that aren't loaded

* Make ARMJIT_Memory::DeInit more robust on the Switch

* Reset MemoryFile on Windows to INVALID_HANDLE_VALUE, not nullptr

- There is a difference

* Don't explicitly store a Valid state in GLCompositor or the 3D renderers

- Instead, create them with static methods while making the actual constructors private

* Make initialization of OpenGL resources fail if OpenGL isn't loaded

* assert that OpenGL is loaded instead of returning failure

src/DSi.cpp

@@ -128,6 +128,10 @@ void DeInit()
     delete[] NWRAM_A;
     delete[] NWRAM_B;
     delete[] NWRAM_C;
+
+    NWRAM_A = nullptr;
+    NWRAM_B = nullptr;
+    NWRAM_C = nullptr;
 #endif
 
     DSi_I2C::DeInit();
@@ -135,10 +139,16 @@ void DeInit()
     DSi_AES::DeInit();
     DSi_DSP::DeInit();
 
-    for (int i = 0; i < 8; i++) delete NDMAs[i];
+    for (int i = 0; i < 8; i++)
+    {
+        delete NDMAs[i];
+        NDMAs[i] = nullptr;
+    }
 
     delete SDMMC;
+    SDMMC = nullptr;
     delete SDIO;
+    SDIO = nullptr;
 }
 
 void Reset()