Shorten dumpsys media.audio_flinger output

Don't include in FastMixer if it's not present.
This removes confusing clutter especially for devices
with a separate deep buffer output thread, or for the
duplicating thread and A2DP output thread.

Change-Id: I84933f5555593256f11ba0895ec915c09cf16963
diff --git a/services/audioflinger/FastMixer.cpp b/services/audioflinger/FastMixer.cpp
index 3bb7b44..3fe50dc 100644
--- a/services/audioflinger/FastMixer.cpp
+++ b/services/audioflinger/FastMixer.cpp
@@ -588,6 +588,10 @@
 
 void FastMixerDumpState::dump(int fd)
 {
+    if (mCommand == FastMixerState::INITIAL) {
+        fdprintf(fd, "FastMixer not initialized\n");
+        return;
+    }
 #define COMMAND_MAX 32
     char string[COMMAND_MAX];
     switch (mCommand) {