Remove an assert in Bullet for the Character physics.

This assert happens all the time for character physics in debug mode.
In release mode, the assert is skipped but the code is still incorrect
although it does not cause any crash strangely.

extern/bullet2/src/BulletDynamics/Character/btKinematicCharacterController.cpp

@@ -29,10 +29,13 @@ subject to the following restrictions:
 static btVector3
 getNormalizedVector(const btVector3& v)
 {
-	btVector3 n = v.normalized();
-	if (n.length() < SIMD_EPSILON) {
-		n.setValue(0, 0, 0);
-	}
+    btScalar l = v.length();
+    btVector3 n = v;
+    if (l < SIMD_EPSILON) {
+        n.setValue(0,0,0);
+    } else {
+        n /= l;
+    }
 	return n;
 }