clang-format: Fix crasher on weird comments.

Crashing input:
  /\
  / comment

llvm-svn: 226454
diff --git a/clang/unittests/Format/FormatTest.cpp b/clang/unittests/Format/FormatTest.cpp
index f267c94..615b46a 100644
--- a/clang/unittests/Format/FormatTest.cpp
+++ b/clang/unittests/Format/FormatTest.cpp
@@ -1035,6 +1035,9 @@
                    "     // spanning two lines\n"
                    " x + 3) {\n"
                    "}"));
+
+  verifyNoCrash("/\\\n/");
+  verifyNoCrash("/\\\n* */");
 }
 
 TEST_F(FormatTest, KeepsParameterWithTrailingCommentsOnTheirOwnLine) {