Fix json cycle issue in NCS

Author: amidgol

dotnet_3/cs/rest/NCS/Controllers/NcsRestController.cs

@@ -43,7 +43,7 @@ public IActionResult Expint(int n, double x)
             }
             catch (Exception e)
             {
-                return BadRequest(e);
+                return BadRequest(e.Message);
             }
         }
 
@@ -64,7 +64,7 @@ public IActionResult Fisher(int m, int n, double x)
             }
             catch (Exception e)
             {
-                return BadRequest(e);
+                return BadRequest(e.Message);
             }
         }
 
@@ -84,7 +84,7 @@ public IActionResult Gammq(double a, double x)
             }
             catch (Exception e)
             {
-                return BadRequest(e);
+                return BadRequest(e.Message);
             }
         }