Mesh on spline with bIsDynamicObstacle enabled causes error on server start

Hi,

It appears when you use a mesh with **bIsDynamicObstacle ** on a spline the server will throw an error on start

See error below:

[2017.11.15-02.14.47:160][  0]LogOutputDevice: Error: 
[2017.11.15-02.14.47:160][  0]LogOutputDevice: Error: [Callstack]  20  0x000000000231473e  /home/Binaries/Linux/XServer() [0x231473e]
[2017.11.15-02.14.47:160][  0]LogOutputDevice: Error: [Callstack]  19  0x00007f7ef39471c1  /lib/x86_64-linux-gnu/libc.so.6(__libc_start_main+0xf1) [0x7f7ef39471c1]
[2017.11.15-02.14.47:160][  0]LogOutputDevice: Error: [Callstack]  18  0x00000000055a0194  CommonLinuxMain(int, char**, int (*)(wchar_t const*))
[2017.11.15-02.14.47:160][  0]LogOutputDevice: Error: [Callstack]  17  0x0000000002321677  GuardedMain(wchar_t const*)
[2017.11.15-02.14.47:160][  0]LogOutputDevice: Error: [Callstack]  16  0x000000000231aa13  FEngineLoop::Init()
[2017.11.15-02.14.47:160][  0]LogOutputDevice: Error: [Callstack]  15  0x00000000046ba23e  UGameEngine::Start()
[2017.11.15-02.14.47:160][  0]LogOutputDevice: Error: [Callstack]  14  0x00000000046e63d9  UGameInstance::StartGameInstance()
[2017.11.15-02.14.47:160][  0]LogOutputDevice: Error: [Callstack]  13  0x0000000004e45e70  UEngine::Browse(FWorldContext&, FURL, FString&)
[2017.11.15-02.14.47:160][  0]LogOutputDevice: Error: [Callstack]  12  0x0000000004e49ccd  UEngine::LoadMap(FWorldContext&, FURL, UPendingNetGame*, FString&)
[2017.11.15-02.14.47:160][  0]LogOutputDevice: Error: [Callstack]  11  0x000000000422fde0  UNavigationSystem::OnWorldInitDone(FNavigationSystemRunMode)
[2017.11.15-02.14.47:160][  0]LogOutputDevice: Error: [Callstack]  10  0x000000000422dd28  UNavigationSystem::ConditionalPopulateNavOctree()
[2017.11.15-02.14.47:160][  0]LogOutputDevice: Error: [Callstack]  09  0x000000000422ece0  UNavigationSystem::AddElementToNavOctree(FNavigationDirtyElement const&)
[2017.11.15-02.14.47:160][  0]LogOutputDevice: Error: [Callstack]  08  0x00000000042083a1  FNavigationOctree::AddNode(UObject*, INavRelevantInterface*, FBox const&, FNavigationOctreeElement&)
[2017.11.15-02.14.47:160][  0]LogOutputDevice: Error: [Callstack]  07  0x000000000427e00d  TBaseStaticDelegateInstance<void (UActorComponent*, FNavigationRelevantData&)>::ExecuteIfSafe(UActorComponent*, FNavigationRelevantData&) const
[2017.11.15-02.14.47:160][  0]LogOutputDevice: Error: [Callstack]  06  0x00000000042acbe5  FRecastNavMeshGenerator::ExportComponentGeometry(UActorComponent*, FNavigationRelevantData&)
[2017.11.15-02.14.47:160][  0]LogOutputDevice: Error: [Callstack]  05  0x00000000045b6ce5  USplineMeshComponent::DoCustomNavigableGeometryExport(FNavigableGeometryExport&) const
[2017.11.15-02.14.47:160][  0]LogOutputDevice: Error: [Callstack]  04  0x00000000024c413f  FDebug::OptionallyLogFormattedEnsureMessageReturningFalse(bool, char const*, char const*, int, wchar_t const*, ...)
[2017.11.15-02.14.47:160][  0]LogOutputDevice: Error: [Callstack]  03  0x00000000024d7965  FDebug::EnsureFailed(char const*, char const*, int, wchar_t const*)
[2017.11.15-02.14.47:160][  0]LogOutputDevice: Error: [Callstack]  02  0x000000000247cb45  FLinuxPlatformStackWalk::StackWalkAndDumpEx(char*, unsigned long, int, unsigned int, void*)
[2017.11.15-02.14.47:160][  0]LogOutputDevice: Error: [Callstack]  01  0x0000000002366315  FGenericPlatformStackWalk::StackWalkAndDump(char*, unsigned long, int, void*)
[2017.11.15-02.14.47:160][  0]LogOutputDevice: Error: [Callstack]  00  0x000000000247cb7f  FLinuxPlatformStackWalk::CaptureStackBackTrace(unsigned long long*, unsigned int, void*)
[2017.11.15-02.14.47:160][  0]LogOutputDevice: Error: Stack: 
[2017.11.15-02.14.47:160][  0]LogOutputDevice: Error: 
[2017.11.15-02.14.47:160][  0]LogOutputDevice: Error: Ensure condition failed: !NavCollision->bIsDynamicObstacle [File:G:\UnrealSourceBuilt\UnrealEngine-4.17.2-release\Engine\Source\Runtime\Engine\Private\Components\SplineMeshComponent.cpp] [Line: 1037]
[2017.11.15-02.14.47:160][  0]LogOutputDevice: Error: 
[2017.11.15-02.14.47:160][  0]LogOutputDevice: Error: === Handled ensure: ===