[pseudo] Fix an out-of-bound access for LRTable::Actions.

Without this patch, when End == Start, we access Actions[Actions.end()]
though we return an empty result.
This fixes an assertion failure in MSVC STL debug build.

clang/lib/Tooling/Syntax/Pseudo/LRTable.cpp

@@ -112,6 +112,8 @@ llvm::ArrayRef<LRTable::Action> LRTable::find(StateID Src, SymbolID ID) const {
          "subrange of the StateIdx should be sorted!");
   const LRTable::StateID *Start = llvm::partition_point(
       TargetedStates, [&Src](LRTable::StateID S) { return S < Src; });
+  if (Start == TargetedStates.end())
+    return {};
   const LRTable::StateID *End = Start;
   while (End != TargetedStates.end() && *End == Src)
     ++End;