clang-format: [JS] Fix a crash in handledTemplateStrings.

llvm-svn: 281816
diff --git a/clang/lib/Format/FormatTokenLexer.cpp b/clang/lib/Format/FormatTokenLexer.cpp
index 8c795fb..c9670ae 100644
--- a/clang/lib/Format/FormatTokenLexer.cpp
+++ b/clang/lib/Format/FormatTokenLexer.cpp
@@ -235,6 +235,8 @@
     return;
   }
   if (BacktickToken->is(tok::r_brace)) {
+    if (StateStack.size() == 1)
+      return;
     StateStack.pop();
     if (StateStack.top() != LexerState::TEMPLATE_STRING)
       return;