FindVulkan: Fix for SDK versions < 1.0.42 on 32-bit Windows

Before Vulkan 1.0.42, the SDK would add the Bin directory to `PATH`,
which was confusing the 32-bit search on Windows.  Avoid such confusion
by ignoring the `PATH` when looking for the 32-bit version.

Vulkan 1.0.42 fixed the whole problem by moving the libraries into Lib,
Lib32, so this is strictly a compatibility fix for old SDKs.

Modules/FindVulkan.cmake

@@ -48,6 +48,7 @@ if(WIN32)
       PATHS
         "$ENV{VULKAN_SDK}/Lib32"
         "$ENV{VULKAN_SDK}/Bin32"
+        NO_SYSTEM_ENVIRONMENT_PATH
         )
   endif()
 else()