Don't do checksum callbacks if there are no checksums at all

Change-Id: I5eeca4b20b4052a683b93fc75820b79578fbdee6

src/main/java/com/android/tools/r8/dex/DexParser.java

diff --git a/src/main/java/com/android/tools/r8/dex/DexParser.java b/src/main/java/com/android/tools/r8/dex/DexParser.java
index 20678fe..d5e338e 100644
--- a/src/main/java/com/android/tools/r8/dex/DexParser.java
+++ b/src/main/java/com/android/tools/r8/dex/DexParser.java
@@ -715,7 +715,7 @@
       AnnotationsDirectory annotationsDirectory = annotationsDirectoryAt(annotationsOffsets[i]);
 
       Long checksum = null;
-      if (checksums != null) {
+      if (checksums != null && !checksums.isEmpty()) {
         String desc = type.descriptor.toASCIIString();
         checksum = checksums.getOrDefault(desc, null);
         if (!options.dexClassChecksumFilter.test(desc, checksum)) {