MC/COFF: Correctly emit the size of an empty string table.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@144111 91177308-0d34-0410-b5e6-96231b3b80d8
diff --git a/lib/MC/WinCOFFObjectWriter.cpp b/lib/MC/WinCOFFObjectWriter.cpp
index b15e225..4d3b59c 100644
--- a/lib/MC/WinCOFFObjectWriter.cpp
+++ b/lib/MC/WinCOFFObjectWriter.cpp
@@ -281,6 +281,7 @@
   // The string table data begins with the length of the entire string table
   // including the length header. Allocate space for this header.
   Data.resize(4);
+  update_length();
 }
 
 size_t StringTable::size() const {