No need to wrap IOException in C#

Antlr4.Runtime/UnbufferedCharStream.cs

@@ -238,16 +238,10 @@ namespace Antlr4.Runtime
                 {
                     return i;
                 }
-                try
+
-                {
                 int c = NextChar();
                 Add(c);
             }
-                catch (IOException ioe)
-                {
-                    throw new RuntimeException(ioe);
-                }
-            }
             return n;
         }