Convert some assert(0) to llvm_unreachable or fold an 'if' condition into the assert.

llvm-svn: 211254
diff --git a/llvm/lib/TableGen/Record.cpp b/llvm/lib/TableGen/Record.cpp
index c553a21..f7843dc 100644
--- a/llvm/lib/TableGen/Record.cpp
+++ b/llvm/lib/TableGen/Record.cpp
@@ -811,20 +811,14 @@
   }
   case HEAD: {
     if (ListInit *LHSl = dyn_cast<ListInit>(LHS)) {
-      if (LHSl->getSize() == 0) {
-        assert(0 && "Empty list in car");
-        return nullptr;
-      }
+      assert(LHSl->getSize() != 0 && "Empty list in car");
       return LHSl->getElement(0);
     }
     break;
   }
   case TAIL: {
     if (ListInit *LHSl = dyn_cast<ListInit>(LHS)) {
-      if (LHSl->getSize() == 0) {
-        assert(0 && "Empty list in cdr");
-        return nullptr;
-      }
+      assert(LHSl->getSize() != 0 && "Empty list in cdr");
       // Note the +1.  We can't just pass the result of getValues()
       // directly.
       ArrayRef<Init *>::iterator begin = LHSl->getValues().begin()+1;