throw an error when finding invalid argument specifier

src/number.c

@@ -198,7 +198,7 @@ pic_number_atan(pic_state *pic)
   double f,g;
   int argc;
 
-  argc = pic_get_args(pic, "f|g", &f, &g);
+  argc = pic_get_args(pic, "f|f", &f, &g);
   if (argc == 1) {
     f = atan(f);
     return pic_float_value(f);

src/vm.c

@@ -74,6 +74,10 @@ pic_get_args(pic_state *pic, const char *format, ...)
 	}
       }
       break;
+    default:
+      {
+	pic_error(pic, "pic_get_args: invalid argument specifier given");
+      }
     }
   }
   if (argc > i) {