BitcodeReader: Allow METADATA_STRINGS to only have !""

Support parsing a METADATA_STRINGS record that only has a single piece
of metadata, !"".  Fixes a corner case in r264551.

llvm-svn: 264699
diff --git a/llvm/lib/Bitcode/Reader/BitcodeReader.cpp b/llvm/lib/Bitcode/Reader/BitcodeReader.cpp
index cb2784f..72ac217 100644
--- a/llvm/lib/Bitcode/Reader/BitcodeReader.cpp
+++ b/llvm/lib/Bitcode/Reader/BitcodeReader.cpp
@@ -1899,7 +1899,7 @@
   unsigned StringsOffset = Record[1];
   if (!NumStrings)
     return error("Invalid record: metadata strings with no strings");
-  if (StringsOffset >= Blob.size())
+  if (StringsOffset > Blob.size())
     return error("Invalid record: metadata strings corrupt offset");
 
   StringRef Lengths = Blob.slice(0, StringsOffset);