fix a crash I introduced, thanks to Ted for the awesome reduced
testcase :)


git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@63182 91177308-0d34-0410-b5e6-96231b3b80d8
diff --git a/Driver/DependencyFile.cpp b/Driver/DependencyFile.cpp
index 0d4ee91..673ca07 100644
--- a/Driver/DependencyFile.cpp
+++ b/Driver/DependencyFile.cpp
@@ -174,8 +174,11 @@
   // #line markers to affect dependency generation!
   SourceManager &SM = PP->getSourceManager();
   
-  FileID FID = SM.getFileID(SM.getInstantiationLoc(Loc));
-  const char *Filename = SM.getFileEntryForID(FID)->getName();
+  const FileEntry *FE =
+    SM.getFileEntryForID(SM.getFileID(SM.getInstantiationLoc(Loc)));
+  if (FE == 0) return;
+  
+  const char *Filename = FE->getName();
   if (!FileMatchesDepCriteria(Filename, FileType))
     return;