[llvm] Use pop_back_val (NFC)

llvm/lib/Bitcode/Reader/BitcodeReader.cpp

@@ -2933,8 +2933,7 @@ Error BitcodeReader::parseUseLists() {
       if (RecordLength < 3)
         // Records should have at least an ID and two indexes.
         return error("Invalid record");
-      unsigned ID = Record.back();
-      Record.pop_back();
+      unsigned ID = Record.pop_back_val();
 
       Value *V;
       if (IsBB) {