Implement IAllSystemAppletProxiesService: 350 (OpenSystemApplicationProxy) (#237)

Implements IAllSystemAppletProxiesService: 350
(OpenSystemApplicationProxy)

This fixes a crash that occurs when launching an NSP forwarder generated
by Nro2Nsp.

src/Ryujinx.HLE/HOS/Services/Am/AppletAE/IAllSystemAppletProxiesService.cs

@@ -1,4 +1,5 @@
 using Ryujinx.HLE.HOS.Services.Am.AppletAE.AllSystemAppletProxiesService;
+using Ryujinx.HLE.HOS.Services.Am.AppletOE.ApplicationProxyService;
 
 namespace Ryujinx.HLE.HOS.Services.Am.AppletAE
 {
@@ -25,5 +26,14 @@ namespace Ryujinx.HLE.HOS.Services.Am.AppletAE
 
             return ResultCode.Success;
         }
+
+        [CommandCmif(350)]
+        // OpenSystemApplicationProxy(u64, pid, handle<copy>) -> object<nn::am::service::IApplicationProxy>
+        public ResultCode OpenSystemApplicationProxy(ServiceCtx context)
+        {
+            MakeObject(context, new IApplicationProxy(context.Request.HandleDesc.PId));
+
+            return ResultCode.Success;
+        }
     }
 }