don't pass null string to CFRelease.

Author: padenot

src/cubeb_audiounit.cpp

@@ -3159,14 +3159,14 @@ audiounit_create_device_from_hwdev(cubeb_device_info * ret, AudioObjectID devid,
 
     if (str) {
       ret->friendly_name = audiounit_strref_to_cstr_utf8(str);
+      CFRelease(str);
     } else {
       // Couldn't get a friendly_name, nor a datasource name, return a valid
       // string of length 0.
       char * fallback_name = new char[1];
       fallback_name[0] = '\0';
       ret->friendly_name = fallback_name;
     }
-    CFRelease(str);
   }
 
   size = sizeof(CFStringRef);