Fix issue #277 - error due to hits hitting nHCal corners (#284)

Signed-off-by: lkosarz <[email protected]>

### Briefly, what does this PR introduce?
Fixes segmentation issue due to polyhedra corners sticking out of rmax.

### What kind of change does this PR introduce?
- [x] Bug fix (issue #277)
- [ ] New feature (issue #__)
- [ ] Documentation update
- [ ] Other: __

### Please check if this PR fulfills the following:
- [ ] Tests for the changes have been added
- [ ] Documentation has been added / updated
- [ ] Changes have been communicated to collaborators @lkosarz 

### Does this PR introduce breaking changes? What changes might users
need to make to their code?
No.

### Does this PR change default behavior?
No.

Signed-off-by: lkosarz <[email protected]>
Co-authored-by: lkosarz <[email protected]>

compact/hcal/backward.xml

@@ -6,8 +6,9 @@
     <constant name="HcalEndcapNSteelThickness"       value="4.0 * cm"/>
     <constant name="HcalEndcapNPolystyreneThickness" value="0.4 * cm"/>
 
+    <constant name="HcalEndcapN_polyhedron_rmax"     value="251.444*cm"/>
     <constant name="HcalEndcapN_segments_rmin"     value="19.9431*cm"/>
-    <constant name="HcalEndcapN_segments_rmax"     value="251.444*cm"/>
+    <constant name="HcalEndcapN_segments_rmax"     value="HcalEndcapN_polyhedron_rmax/(cos(180*deg/HcalEndcapN_CaloSides))"/>
 
     <documentation>
       - Hcal Endcap N Layers and computed Thickness
@@ -37,8 +38,8 @@
         numsides="HcalEndcapN_CaloSides"
         zmin="HcalEndcapN_zmin"
         rmin="HcalEndcapN_segments_rmin"
-        rmax="HcalEndcapN_segments_rmax"/>
-      <layer repeat="HcalEndcapNLayer_NRepeat" vis="HcalEndcapLayerVis" >
+        rmax="HcalEndcapN_polyhedron_rmax"/>
+      <layer repeat="HcalEndcapNLayer_NRepeat" vis="HcalEndcapLayerVis">
         <slice material="Steel235" thickness="HcalEndcapNSteelThickness" vis="HcalAbsorberVis"/>
         <slice material="Polystyrene" thickness="HcalEndcapNPolystyreneThickness" vis="HcalSensorVis" sensitive="yes" limits="cal_limits"/>
       </layer>