error if invalid radius

Waveguides/waveguide2D_Hbend.geo

@@ -8,6 +8,11 @@
 
 Include "waveguide2D_Hbend.dat" ;
 
+If(R < W/2 + 1e-3)
+  Error("Invalid radius");
+  R = W/2 + 1e-3;
+EndIf
+
 p[] += newp ; Point(newp) = {0, R, 0, res} ;
 p[] += newp ; Point(newp) = {-L,-W/2, 0, res} ;
 p[] += newp ; Point(newp) = { 0,-W/2, 0, res} ;