Fix dex file reading in VdexFile::GetNextDexFileData.

Dex files in a vdex file are always aligned.

bug: 64527414
Test: run-test --random-profile 663-odd-dex-size
Change-Id: I1e3b36e04b35ad3128eebee86f3166788162dec5
diff --git a/test/663-odd-dex-size/expected.txt b/test/663-odd-dex-size/expected.txt
new file mode 100644
index 0000000..3da1ec2
--- /dev/null
+++ b/test/663-odd-dex-size/expected.txt
@@ -0,0 +1 @@
+HelloWorld