[TableGen] Replace some calls to ListInit::getSize() with ListInit::empty() if it was just comparing to 0. NFC.

llvm-svn: 237340
diff --git a/llvm/lib/TableGen/TGParser.cpp b/llvm/lib/TableGen/TGParser.cpp
index 56f156d..23ef535 100644
--- a/llvm/lib/TableGen/TGParser.cpp
+++ b/llvm/lib/TableGen/TGParser.cpp
@@ -841,7 +841,7 @@
           return nullptr;
         }
 
-        if (LHSl && LHSl->getSize() == 0) {
+        if (LHSl && LHSl->empty()) {
           TokError("empty list argument in unary operator");
           return nullptr;
         }