Finishing roundNGon's parameter checking

scad/util/common.scad

 
+assertDiameterMsg = "diameter out of range[ >= 0 ]";
 
 
 /**
@@ -48,6 +49,11 @@ module roundRect(w, h, r) {
   * `r` corner radius
   */
 module roundNGon(d, n, r) {
+  
+  assert(d >= 0, assertDiameterMsg);
+  assert(r > 0 && r < d/2, "radius out of range[ 0 < r < d/2 ]");
+  assert(n > 2, "corner count out of range[ > 2 ]");
+  
   minkowski() {
     circle(d=d - 2*r, $fn=n);
     if (r > 0) circle(r=r);