Fix priority scheduling logic

This resolves sync loads not being properly prioritised.

patches/server/Moonrise-optimisation-patches.patch

@@ -12165,7 +12165,7 @@ index 0000000000000000000000000000000000000000..00000000000000000000000000000000
 +            return us == null ? dfl : us;
 +        }
 +        if (us == null) {
-+            return dfl;
++            return neighbour;
 +        }
 +
 +        return PrioritisedExecutor.Priority.max(us, neighbour);
@@ -12211,7 +12211,7 @@ index 0000000000000000000000000000000000000000..00000000000000000000000000000000
 +
 +    // must hold scheduling lock
 +    public void raisePriority(final PrioritisedExecutor.Priority priority) {
-+        if (this.priority == null || this.priority.isHigherOrEqualPriority(priority)) {
++        if (this.priority != null && this.priority.isHigherOrEqualPriority(priority)) {
 +            return;
 +        }
 +        this.setPriority(priority);
@@ -12242,7 +12242,7 @@ index 0000000000000000000000000000000000000000..00000000000000000000000000000000
 +
 +    // must hold scheduling lock
 +    public void lowerPriority(final PrioritisedExecutor.Priority priority) {
-+        if (this.priority == null || this.priority.isLowerOrEqualPriority(priority)) {
++        if (this.priority != null && this.priority.isLowerOrEqualPriority(priority)) {
 +            return;
 +        }
 +        this.setPriority(priority);