Fix clang-format segfault.

When annotating "lines" starting with ":", clang-format would segfault.
This could actually happen in valid code, e.g.
  #define A :

git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@177283 91177308-0d34-0410-b5e6-96231b3b80d8

lib/Format/TokenAnnotator.cpp

@@ -319,6 +319,8 @@ private:
         Tok->Type = TT_ObjCMethodSpecifier;
       break;
     case tok::colon:
+      if (Tok->Parent == NULL)
+        return false;
       // Colons from ?: are handled in parseConditional().
       if (Tok->Parent->is(tok::r_paren) && Contexts.size() == 1) {
         Tok->Type = TT_CtorInitializerColon;

unittests/Format/FormatTest.cpp

@@ -1068,6 +1068,8 @@ TEST_F(FormatTest, EmptyLinesInMacroDefinitions) {
 }
 
 TEST_F(FormatTest, MacroDefinitionsWithIncompleteCode) {
+  verifyFormat("#define A :");
+
   // FIXME: Improve formatting of case labels in macros.
   verifyFormat("#define SOMECASES  \\\n"
                "case 1:            \\\n"