[clang-tidy] Fix crashing altera-struct-pack-align on invalid RecordDecls

Reviewed-By: martong

Differential Revision: https://reviews.llvm.org/D114256
diff --git a/clang-tools-extra/clang-tidy/altera/StructPackAlignCheck.cpp b/clang-tools-extra/clang-tidy/altera/StructPackAlignCheck.cpp
index ef5fe41..6ae5351 100644
--- a/clang-tools-extra/clang-tidy/altera/StructPackAlignCheck.cpp
+++ b/clang-tools-extra/clang-tidy/altera/StructPackAlignCheck.cpp
@@ -51,6 +51,10 @@
   if (Struct->isTemplated())
      return;
 
+  // Packing and alignment requirements for invalid decls are meaningless.
+  if (Struct->isInvalidDecl())
+    return;
+
   // Get sizing info for the struct.
   llvm::SmallVector<std::pair<unsigned int, unsigned int>, 10> FieldSizes;
   unsigned int TotalBitSize = 0;