Don't override existing host thread priorities

If the thread that's hosting yabridge's plugin is already using realtime
scheduling.

src/common/utils.cpp

@@ -32,6 +32,16 @@ fs::path get_temporary_directory() {
 }
 
 bool set_realtime_priority(bool sched_fifo) {
+    // If we're already using SCHED_FIFO then this is likely set by the host,
+    // and we should not make any additional changes
+    if (sched_fifo) {
+        sched_param current_params{};
+        if (sched_getparam(0, &current_params) == 0 &&
+            current_params.sched_priority > 0) {
+            return true;
+        }
+    }
+
     sched_param params{.sched_priority = 5};
     return sched_setscheduler(0, sched_fifo ? SCHED_FIFO : SCHED_OTHER,
                               &params) == 0;