Solve race condition between AThousandShips and Akien

Solves race condition between AThousandShips and Akien.

doc/classes/NavigationAgent3D.xml

@@ -168,7 +168,7 @@
 			The height of the avoidance agent. Agents will ignore other agents or obstacles that are above or below their current position + height in 2D avoidance. Does nothing in 3D avoidance which uses radius spheres alone.
 		</member>
 		<member name="keep_y_velocity" type="bool" setter="set_keep_y_velocity" getter="get_keep_y_velocity" default="true">
-			If [code]true[/code] and the agent uses 2D avoidance it will remember the set y-axis velocity and reapply it after the avoidance step. While 2D avoidance has no y-axis and simulates on a flat plane this setting can help mitigate the most obvious clipping on uneven 3D geometry.
+			If [code]true[/code], and the agent uses 2D avoidance, it will remember the set y-axis velocity and reapply it after the avoidance step. While 2D avoidance has no y-axis and simulates on a flat plane this setting can help mitigate the most obvious clipping on uneven 3D geometry.
 		</member>
 		<member name="max_neighbors" type="int" setter="set_max_neighbors" getter="get_max_neighbors" default="10">
 			The maximum number of neighbors for the agent to consider.

scene/3d/navigation_agent_3d.cpp

@@ -311,11 +311,9 @@ void NavigationAgent3D::_notification(int p_what) {
 }
 
 void NavigationAgent3D::_validate_property(PropertyInfo &p_property) const {
-	if (p_property.name == "keep_y_velocity") {
-		if (use_3d_avoidance) {
-			p_property.usage = PROPERTY_USAGE_NONE;
-			return;
-		}
+	if (p_property.name == "keep_y_velocity" && use_3d_avoidance) {
+		p_property.usage = PROPERTY_USAGE_NONE;
+		return;
 	}
 }