Kernel/IPC: Support translation of null handles

Missed this in my first implementation. Thanks to @wwylele for pointing
out that this was missing.

src/core/hle/kernel/hle_ipc.cpp

@@ -67,11 +67,14 @@ ResultCode HLERequestContext::PopulateFromIncomingCommandBuffer(const u32_le* sr
             ASSERT(i + num_handles <= command_size); // TODO(yuriks): Return error
             for (u32 j = 0; j < num_handles; ++j) {
                 Handle handle = src_cmdbuf[i];
-                SharedPtr<Object> object = src_table.GetGeneric(handle);
+                SharedPtr<Object> object = nullptr;
+                if (handle != 0) {
+                    object = src_table.GetGeneric(handle);
                     ASSERT(object != nullptr); // TODO(yuriks): Return error
                     if (descriptor == IPC::DescriptorType::MoveHandle) {
                         src_table.Close(handle);
                     }
+                }
 
                 cmd_buf[i++] = AddOutgoingHandle(std::move(object));
             }
@@ -112,9 +115,11 @@ ResultCode HLERequestContext::WriteToOutgoingCommandBuffer(u32_le* dst_cmdbuf, P
             ASSERT(i + num_handles <= command_size);
             for (u32 j = 0; j < num_handles; ++j) {
                 SharedPtr<Object> object = GetIncomingHandle(cmd_buf[i]);
-
+                Handle handle = 0;
+                if (object != nullptr) {
                     // TODO(yuriks): Figure out the proper error handling for if this fails
-                Handle handle = dst_table.Create(object).Unwrap();
+                    handle = dst_table.Create(object).Unwrap();
+                }
                 dst_cmdbuf[i++] = handle;
             }
             break;

src/tests/core/hle/kernel/hle_ipc.cpp

@@ -94,6 +94,18 @@ TEST_CASE("HLERequestContext::PopoulateFromIncomingCommandBuffer", "[core][kerne
         REQUIRE(context.GetIncomingHandle(output[5]) == c);
     }
 
+    SECTION("translates null handles") {
+        const u32_le input[]{
+            IPC::MakeHeader(0, 0, 2), IPC::MoveHandleDesc(1), 0,
+        };
+
+        auto result = context.PopulateFromIncomingCommandBuffer(input, *process, handle_table);
+
+        REQUIRE(result == RESULT_SUCCESS);
+        auto* output = context.CommandBuffer();
+        REQUIRE(context.GetIncomingHandle(output[2]) == nullptr);
+    }
+
     SECTION("translates CallingPid descriptors") {
         const u32_le input[]{
             IPC::MakeHeader(0, 0, 2), IPC::CallingPidDesc(), 0x98989898,
@@ -171,6 +183,17 @@ TEST_CASE("HLERequestContext::WriteToOutgoingCommandBuffer", "[core][kernel]") {
         REQUIRE(handle_table.GetGeneric(output[4]) == b);
     }
 
+    SECTION("translates null handles") {
+        input[0] = IPC::MakeHeader(0, 0, 2);
+        input[1] = IPC::MoveHandleDesc(1);
+        input[2] = context.AddOutgoingHandle(nullptr);
+
+        auto result = context.WriteToOutgoingCommandBuffer(output, *process, handle_table);
+
+        REQUIRE(result == RESULT_SUCCESS);
+        REQUIRE(output[2] == 0);
+    }
+
     SECTION("translates multi-handle descriptors") {
         auto a = MakeObject();
         auto b = MakeObject();