[clang] [Clang] prevent null explicit object argument from being deduced (PR #104328)

[Oleksandr T. via cfe-commits]

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@@ -4462,6 +4462,9 @@ TemplateDeductionResult Sema::DeduceTemplateArguments(
       ParamTypesForArgChecking.push_back(ParamType);
 
       if (ParamIdx == 0 && HasExplicitObject) {
+        if (ObjectType.isNull())
+          return TemplateDeductionResult::InvalidExplicitArguments;
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a-tarasyuk wrote:

@mizvekov thanks for your feedback. I assumed `TemplateDeductionResult::AlreadyDiagnosed` was intended for situations where the checker has already detected errors. Is it? Should I revert these changes, or would opening a new issue/PR be better?

/cc @cor3ntin 

https://github.com/llvm/llvm-project/pull/104328