[clang] [Clang][Sema] Fix crash in CheckNonTypeTemplateParameterType with invalid type (PR #186200)

[Krystian Stasiowski via cfe-commits]

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@@ -1342,7 +1342,10 @@ QualType Sema::CheckNonTypeTemplateParameterType(TypeSourceInfo *&TSI,
     //    - an identifier associated by name lookup with a non-type
     //      template-parameter declared with a type that contains a
     //      placeholder type (7.1.7.4),
-    TSI = SubstAutoTypeSourceInfoDependent(TSI);
+    TypeSourceInfo *NewTSI = SubstAutoTypeSourceInfoDependent(TSI);
+    if (!NewTSI)
+      return QualType();
+    TSI = NewTSI;
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sdkrystian wrote:

`SubstAutoTypeSourceInfoDependent` won't modify `TSI`. It returns `TSI` unchanged if there is nothing to transform, a new `TypeSourceInfo` if substitution was performed and succeeded, or `nullptr` if it fails.

https://github.com/llvm/llvm-project/pull/186200