Handle zero-length debug directory entries.

Part of https://reviews.llvm.org/D51652 (tests will be in the lld repo)

llvm-svn: 341485
diff --git a/llvm/tools/llvm-readobj/COFFDumper.cpp b/llvm/tools/llvm-readobj/COFFDumper.cpp
index c0579d6..4b6125e 100644
--- a/llvm/tools/llvm-readobj/COFFDumper.cpp
+++ b/llvm/tools/llvm-readobj/COFFDumper.cpp
@@ -751,7 +751,7 @@
         W.printNumber("PDBAge", DebugInfo->PDB70.Age);
         W.printString("PDBFileName", PDBFileName);
       }
-    } else {
+    } else if (D.SizeOfData != 0) {
       // FIXME: Type values of 12 and 13 are commonly observed but are not in
       // the documented type enum.  Figure out what they mean.
       ArrayRef<uint8_t> RawData;