Change iftable to never be null

Simplifies code generation by removing a null check. The null case
is rare.

Ritzperf code size: 13107624 -> 13095336

Also addressed comments from previous CL.

Bug: 32577579

Test: test-art-host, run ritzperf both with CC

Change-Id: I2b31e800867112869d7f0643e16c08826296979e
diff --git a/runtime/interpreter/unstarted_runtime.cc b/runtime/interpreter/unstarted_runtime.cc
index 2257fd6..a5b1038 100644
--- a/runtime/interpreter/unstarted_runtime.cc
+++ b/runtime/interpreter/unstarted_runtime.cc
@@ -424,7 +424,7 @@
 
   std::unique_ptr<ZipArchive> zip_archive(ZipArchive::Open(jar_file.c_str(), error_msg));
   if (zip_archive == nullptr) {
-    return nullptr;;
+    return nullptr;
   }
   std::unique_ptr<ZipEntry> zip_entry(zip_archive->Find(entry_name, error_msg));
   if (zip_entry == nullptr) {