clang-format: [JS] Fix bug in regex literal parsing.

The lexer wasn't properly reset leading to unexpected deletions.

llvm-svn: 241262
diff --git a/clang/unittests/Format/FormatTestJS.cpp b/clang/unittests/Format/FormatTestJS.cpp
index 83c2118..40a2a1f 100644
--- a/clang/unittests/Format/FormatTestJS.cpp
+++ b/clang/unittests/Format/FormatTestJS.cpp
@@ -631,6 +631,7 @@
             "var x = 0;",
             format("var regex = /\\/*/;\n"
                    "var x=0;"));
+  EXPECT_EQ("var x = /a\\//;", format("var x = /a\\//  \n;"));
   verifyFormat("var regex = /\"/;", getGoogleJSStyleWithColumns(16));
   verifyFormat("var regex =\n"
                "    /\"/;",