deny direct access to symmed register - prevents bugs

crsn_screen/src/exec.rs

@@ -168,8 +168,8 @@ impl OpTrait for ScreenOp {
                                 let xval = xf.round() as u64;
                                 let yval = yf.round() as u64;
 
-                                state.write(*x, xval);
-                                state.write(*y, yval);
+                                state.write(*x, xval)?;
+                                state.write(*y, yval)?;
                             }
                         }
                     }

crsn_screen/src/parse.rs

@@ -1,4 +1,4 @@
-use crsn::asm::data::{Rd, RdData};
+use crsn::asm::data::{Rd};
 use crsn::asm::error::CrsnError;
 use crsn::asm::instr::op::OpKind;
 use crsn::asm::parse::arg_parser::TokenParser;