Fix loading empty structs from structured buffers (#6439)

Closes #5751

Author: expipiplus1

source/slang/slang-ir-legalize-types.cpp

@@ -2149,6 +2149,12 @@ static LegalVal legalizeInst(
         // This case should only happen when compiling for a target that does not support
         // GpuForeach
         return LegalVal();
+    case kIROp_StructuredBufferLoad:
+        // empty types are removed, so we need to make sure that we're still
+        // loading a none type when we try and load from a to-be-optimized
+        // out structured buffer
+        SLANG_ASSERT(type.flavor == LegalType::Flavor::none);
+        return LegalVal();
     default:
         // TODO: produce a user-visible diagnostic here
         SLANG_UNEXPECTED("non-simple operand(s)!");