AudioStream: fix invalid memory access

Fix AudioStream::getDeviceName() that calls pa_stream_get_device_name()
without checking the return value.
This last can be the error -PA_ERR_NOTSUPPORTED or null for other issues.
In such cases we return an empty string.

Change-Id: Ia293ff8d93212d87c8fa5e6ce8399964044d530f

src/media/audio/pulseaudio/audiostream.h

@@ -83,7 +83,10 @@ class AudioStream {
         }
 
         inline std::string getDeviceName() const {
-            return pa_stream_get_device_name(audiostream_);
+            auto res = pa_stream_get_device_name(audiostream_);
+            if (res == reinterpret_cast<decltype(res)>(-PA_ERR_NOTSUPPORTED) or !res)
+                return {};
+            return res;
         }
 
         bool isReady();