Resolve SDV reported "defect"

NdisMGetDeviceProperty() should always return non-NULL
FunctionalDeviceObject according to _Outptr_opt_. An explicit
FunctionalDeviceObject NULL check has been added to keep the SDV happy
and not calling our driver "defective".

Signed-off-by: Simon Rozman <simon@rozman.si>

README.md

@@ -51,6 +51,8 @@ msbuild wintun.proj [/t:<target>]
 
   - `SDV`: Runs Static Driver Verifier, which includes a clean driver build, only for AMD64 release configuration.
 
+  - `SDVView`: Views the results of the Static Driver Verifier.
+
   - `DVL`: Runs the `SDV`, and creates a Driver Verification Log, only for AMD64 release configurations.
 
   - `MSM`: Builds Microsoft Installer Merge Modules in `<output folder>\wintun-<platform>-<version>.msm`. Requires WHQL signed driver.

wintun.c

@@ -930,6 +930,8 @@ TunInitializeEx(
     Ctx->MiniportAdapterHandle = MiniportAdapterHandle;
 
     NdisMGetDeviceProperty(MiniportAdapterHandle, NULL, &Ctx->FunctionalDeviceObject, NULL, NULL, NULL);
+    if (Status = NDIS_STATUS_FAILURE, !Ctx->FunctionalDeviceObject)
+        goto cleanupFreeCtx;
     /* Reverse engineering indicates that we'd be better off calling
      * NdisWdfGetAdapterContextFromAdapterHandle(functional_device),
      * which points to our TUN_CTX object directly, but this isn't