Tighten diagnoseConflictingDescriptorHeapStrideOptions doc comment (#11723)

Match the comment to the actual condition: the conflict is between a non-zero
explicit -spirv-resource-heap-stride and the unified stride; an explicit stride
of 0 selects the same default OpConstantSizeOfEXT path the unified option
modifies and is not a conflict.

Author: nv-slang-bot[bot]

source/slang/slang-emit-spirv.cpp

@@ -7310,8 +7310,9 @@ struct SPIRVEmitContext : public SourceEmitterBase, public SPIRVEmitSharedContex
     }
 
     // Diagnoses the mutually-exclusive `-spirv-resource-heap-stride` / unified-stride option pair:
-    // an explicit literal stride and the unified maximum stride contradict, so passing both is an
-    // error rather than letting one silently win.
+    // a non-zero explicit literal stride and the unified maximum stride contradict, so combining
+    // them is an error rather than letting one silently win. An explicit stride of 0 selects the
+    // same default `OpConstantSizeOfEXT` path the unified option modifies, so it is not a conflict.
     void diagnoseConflictingDescriptorHeapStrideOptions()
     {
         if (isUnifiedResourceHeapStrideEnabled() &&