Fix the NaCl bitstream reader to report fatal errors.

lib/Bitcode/NaCl/Reader/NaClBitCodes.cpp

 //===- NaClBitcodeHeader.cpp ----------------------------------------------===//
 //     PNaCl bitcode header reader.
 //
 //                     The LLVM Compiler Infrastructure
 //
 // This file is distributed under the University of Illinois Open Source
 // License. See LICENSE.TXT for details.
 //
 //===----------------------------------------------------------------------===//
 //
@@ skipping 102 matching lines @@
     }
     Abbrev->OperandList.push_back(Op);
   }
   return Abbrev;
 }
 
 bool NaClBitCodeAbbrev::isValid() const {
   // Verify that an array op appears can only appear if it is the
   // second to last element.
   unsigned NumOperands = getNumOperandInfos();
+  if (NumOperands == 0) return false;
   for (unsigned i = 0; i < NumOperands; ++i) {
     const NaClBitCodeAbbrevOp &Op = getOperandInfo(i);
     if (Op.isArrayOp() && i + 2 != NumOperands)
       return false;
   }
   return true;
 }