Throw exception when attempting to build empty AudioMixingRule.

This fixes
android.media.audio.cts.AudioPlaybackCaptureTest#testMatchNothing.

The test asserts that attempting to capture playback with no
criteria specified throws and Exception. However, the reason why
the test was passing and Exception thrown was not because of
explicit check for empty AudioMixingRule, but because of
invalid mix role (not adding any rules prior to ag/20001744
caused mix type not to be inferred). If the mix role was
explicitly set for the AudioMixingRule.Builder the test would
also fail the expectation.
This cl is adding explicit check for the presence of rules when
building AudioMixingRule to fix this.

Bug: 252822301
Test: atest AudioPlaybackCaptureTest
Change-Id: If3caa635b67eca779bb2026d2da1c4727e4636e9

media/java/android/media/audiopolicy/AudioMixingRule.java

@@ -704,8 +704,12 @@ public class AudioMixingRule {
          * Combines all of the matching and exclusion rules that have been set and return a new
          * {@link AudioMixingRule} object.
          * @return a new {@link AudioMixingRule} object
+         * @throws IllegalArgumentException if the rule is empty.
          */
         public AudioMixingRule build() {
+            if (mCriteria.isEmpty()) {
+                throw new IllegalArgumentException("Cannot build AudioMixingRule with no rules.");
+            }
             return new AudioMixingRule(
                     mTargetMixType == AudioMix.MIX_TYPE_INVALID
                             ? AudioMix.MIX_TYPE_PLAYERS : mTargetMixType,

media/tests/AudioPolicyTest/src/com/android/audiopolicytest/AudioMixingRuleUnitTests.java

@@ -212,6 +212,12 @@ public class AudioMixingRuleUnitTests {
                 containsInAnyOrder(isAudioMixSessionCriterion(TEST_SESSION_ID)));
     }
 
+    @Test
+    public void audioMixingRuleWithNoRulesFails() {
+        assertThrows(IllegalArgumentException.class,
+                () -> new AudioMixingRule.Builder().build());
+    }
+
 
     private static Matcher isAudioMixUidCriterion(int uid, boolean exclude) {
         return new CustomTypeSafeMatcher<AudioMixMatchCriterion>("uid mix criterion") {