kernelbase: Native machine is optional for IsWow64Process2.

dlls/kernel32/tests/process.c

@@ -2238,6 +2238,12 @@ static void test_IsWow64Process2(void)
     ok(machine == IMAGE_FILE_MACHINE_UNKNOWN, "got %#x\n", machine);
     ok(native_machine == expect_native, "got %#x\n", native_machine);
 
+    SetLastError(0xdeadbeef);
+    machine = 0xdead;
+    ret = pIsWow64Process2(pi.hProcess, &machine, NULL);
+    ok(ret, "IsWow64Process2 error %u\n", GetLastError());
+    ok(machine == IMAGE_FILE_MACHINE_UNKNOWN, "got %#x\n", machine);
+
     ret = TerminateProcess(pi.hProcess, 0);
     ok(ret, "TerminateProcess error\n");
 
@@ -2263,6 +2269,15 @@ static void test_IsWow64Process2(void)
         ok(machine == IMAGE_FILE_MACHINE_UNKNOWN, "got %#x\n", machine);
         ok(native_machine == expect_native, "got %#x\n", native_machine);
     }
+
+    SetLastError(0xdeadbeef);
+    machine = 0xdead;
+    ret = pIsWow64Process2(GetCurrentProcess(), &machine, NULL);
+    ok(ret, "IsWow64Process2 error %u\n", GetLastError());
+    if (is_wow64)
+        ok(machine == IMAGE_FILE_MACHINE_I386, "got %#x\n", machine);
+    else
+        ok(machine == IMAGE_FILE_MACHINE_UNKNOWN, "got %#x\n", machine);
 }
 
 static void test_SystemInfo(void)

dlls/kernelbase/process.c

@@ -899,8 +899,6 @@ BOOL WINAPI DECLSPEC_HOTPATCH IsWow64Process2( HANDLE process, USHORT *machine,
 
     if (wow64)
     {
-        GetNativeSystemInfo( &si );
-
         if (process != GetCurrentProcess())
         {
 #if defined(__i386__) || defined(__x86_64__)
@@ -916,15 +914,22 @@ BOOL WINAPI DECLSPEC_HOTPATCH IsWow64Process2( HANDLE process, USHORT *machine,
             nt = RtlImageNtHeader( NtCurrentTeb()->Peb->ImageBaseAddress );
             *machine = nt->FileHeader.Machine;
         }
+
+        if (!native_machine) return TRUE;
+
+        GetNativeSystemInfo( &si );
     }
     else
     {
+        *machine = IMAGE_FILE_MACHINE_UNKNOWN;
+
+        if (!native_machine) return TRUE;
+
 #ifdef _WIN64
         GetSystemInfo( &si );
 #else
         GetNativeSystemInfo( &si );
 #endif
-        *machine = IMAGE_FILE_MACHINE_UNKNOWN;
     }
 
     switch (si.u.s.wProcessorArchitecture)