Turn an assert into report_fatal_error since it's reachable based on user input

Bug found with AFL fuzz.

llvm-svn: 236076
diff --git a/llvm/lib/Bitcode/Reader/BitstreamReader.cpp b/llvm/lib/Bitcode/Reader/BitstreamReader.cpp
index 2f34532..dff6d18 100644
--- a/llvm/lib/Bitcode/Reader/BitstreamReader.cpp
+++ b/llvm/lib/Bitcode/Reader/BitstreamReader.cpp
@@ -199,7 +199,8 @@
       unsigned NumElts = ReadVBR(6);
 
       // Get the element encoding.
-      assert(i+2 == e && "array op not second to last?");
+      if (i+2 != e)
+       report_fatal_error("Array op not second to last");
       const BitCodeAbbrevOp &EltEnc = Abbv->getOperandInfo(++i);
       if (EltEnc.getEncoding() == BitCodeAbbrevOp::Array ||
           EltEnc.getEncoding() == BitCodeAbbrevOp::Blob)