[UR] Handle INVALID_VALUE in OCL urPlatformGet (#15779)

Pre-commit MR for:
oneapi-src/unified-runtime#2227

As there is a spec change in UR, adapter handling code has been updated
-
it no longer tries to populate the platform list if it would be empty
(otherwise both "destination" pointers could be null, which is now
illegal).

This fixes a bug Intel tracks internally as URT-831

Co-authored-by: Aaron Greig <aaron.greig@codeplay.com>

Author: RossBrunton

sycl/source/detail/adapter.hpp

@@ -100,8 +100,10 @@ class Adapter {
       uint32_t platformCount = 0;
       call<UrApiKind::urPlatformGet>(&MAdapter, 1, 0, nullptr, &platformCount);
       UrPlatforms.resize(platformCount);
-      call<UrApiKind::urPlatformGet>(&MAdapter, 1, platformCount,
-                                     UrPlatforms.data(), nullptr);
+      if (platformCount) {
+        call<UrApiKind::urPlatformGet>(&MAdapter, 1, platformCount,
+                                       UrPlatforms.data(), nullptr);
+      }
       // We need one entry in this per platform
       LastDeviceIds.resize(platformCount);
     });