Fix uninitialized variable warning. NFCI.

llvm-svn: 373450
diff --git a/llvm/lib/Demangle/MicrosoftDemangle.cpp b/llvm/lib/Demangle/MicrosoftDemangle.cpp
index 4be6e5a..8c58254 100644
--- a/llvm/lib/Demangle/MicrosoftDemangle.cpp
+++ b/llvm/lib/Demangle/MicrosoftDemangle.cpp
@@ -2179,7 +2179,7 @@
 
 NodeArrayNode *
 Demangler::demangleTemplateParameterList(StringView &MangledName) {
-  NodeList *Head;
+  NodeList *Head = nullptr;
   NodeList **Current = &Head;
   size_t Count = 0;