Fix loud white nosie after mouse steering (#5812)

* Prevent NaN poisoning in right-mouse rotation (fixes loud thruster sounds and inability to turn)

* Document savebump changes

SAVEBUMP.txt

@@ -13,4 +13,5 @@ Regular tasks
 - data/libs/NameGen.lua: Add new authors to name generator
 
 One-time tasks
+- DynamicBody.cpp: the std::isnan() check in constructor should be removed
 - add your one-time tasks here

src/DynamicBody.cpp

@@ -67,6 +67,12 @@ DynamicBody::DynamicBody(const Json &jsonObj, Space *space) :
 		throw SavedGameCorruptException();
 	}
 
+	// fix saves with nans
+	// SAVEBUMP: This can be removed starting with save version 91
+	if (std::isnan(m_angVel.x) || std::isnan(m_angVel.y) || std::isnan(m_angVel.z)) {
+		m_angVel = vector3d(0.0);
+	}
+
 	m_aiMessage = AIError::AIERROR_NONE;
 	m_decelerating = false;
 }

src/ship/PlayerShipController.cpp

@@ -106,7 +106,9 @@ struct PlayerShipController::Util {
 			auto good_speed = sqrt(2 * max_accel * want_rot) * 0.95;
 			auto frame_speed = want_rot / timeStep;
 			auto tot_speed = std::min(good_speed, frame_speed / 2);
-			rot_vel = (ship_dir.Cross(dir) * c.m_ship->GetOrient()).Normalized() * tot_speed;
+			// this cross product often becomes all-zeros (ship_dir coincides with requested dir)
+			// NormalizedSafe is crucial there to avoid NaN poisoning
+			rot_vel = (ship_dir.Cross(dir) * c.m_ship->GetOrient()).NormalizedSafe() * tot_speed;
 		}
 		return rot_vel;
 	};