pdbdump: Fix crash bug.

pdbdump calls DbiStreamBuilder::commit through PDBFileBuilder::commit
without calling DbiStreamBuilder::finalize. Because `finalize` initializes
`Header` member, `Header` remained nullptr which caused a crash bug.

Differential Revision: https://reviews.llvm.org/D23143

llvm-svn: 277681
diff --git a/llvm/lib/DebugInfo/PDB/Raw/DbiStreamBuilder.cpp b/llvm/lib/DebugInfo/PDB/Raw/DbiStreamBuilder.cpp
index 711295d..b0bb4a0 100644
--- a/llvm/lib/DebugInfo/PDB/Raw/DbiStreamBuilder.cpp
+++ b/llvm/lib/DebugInfo/PDB/Raw/DbiStreamBuilder.cpp
@@ -249,7 +249,10 @@
 }
 
 Error DbiStreamBuilder::commit(const msf::MSFLayout &Layout,
-                               const msf::WritableStream &Buffer) const {
+                               const msf::WritableStream &Buffer) {
+  if (auto EC = finalize())
+    return EC;
+
   auto InfoS =
       WritableMappedBlockStream::createIndexedStream(Layout, Buffer, StreamDBI);