Added PNG48 and PNG64 to the test suite in tests/validate.h

diff --git a/tests/validate.h b/tests/validate.h
index e0c77d5..6e63fe6 100644
--- a/tests/validate.h
+++ b/tests/validate.h
@@ -306,6 +306,8 @@
     { "PNG8", UndefinedCompression, 0.0 },
     { "PNG24", UndefinedCompression, 0.0 },
     { "PNG32", UndefinedCompression, 0.0 },
+    { "PNG48", UndefinedCompression, 0.0 },
+    { "PNG64", UndefinedCompression, 0.0 },
     { "PNM", UndefinedCompression, 0.0 },
     { "PPM", UndefinedCompression, 0.0 },
     { "PREVIEW", UndefinedCompression, 0.0 },