Audio : Fix ASAN crash in VTS test cases

Effect Helper should not try to access min/max values of a tag
when it is not defined.

Bug: 271912230
Test: atest VtsHalAECTargetTest.cpp (with ASAN enabled)

Change-Id: Idf47a521fbd594c83ab0fc21f2750673652b3aee
diff --git a/audio/aidl/vts/EffectHelper.h b/audio/aidl/vts/EffectHelper.h
index f6683cc..831977b 100644
--- a/audio/aidl/vts/EffectHelper.h
+++ b/audio/aidl/vts/EffectHelper.h
@@ -228,10 +228,10 @@
      */
     template <typename S, typename = std::enable_if_t<std::is_arithmetic_v<S>>>
     static std::set<S> expandTestValueBasic(std::set<S>& s) {
-        const auto min = *s.begin(), max = *s.rbegin();
         const auto minLimit = std::numeric_limits<S>::min(),
                    maxLimit = std::numeric_limits<S>::max();
         if (s.size()) {
+            const auto min = *s.begin(), max = *s.rbegin();
             s.insert(min + (max - min) / 2);
             if (min != minLimit) {
                 s.insert(min - 1);