Improve the debug messages when invalid instructions are found

src/core.rs

@@ -53,6 +53,11 @@ impl Core {
                 }
             };
 
+            if instr == 0 {
+                eprintln!("Executing 0 instruction at {:X}", self.pc);
+                break;
+            }
+
             assert_eq!(instr & 3, 3, "Compressed instructions not supported");
 
             let instr = Instruction(instr);
@@ -73,7 +78,7 @@ impl Core {
                     }
                 }
             } else {
-                eprintln!("Invalid Instruction 0x{:08x} 0b{:032b}", instr.0, instr.0);
+                eprintln!("Invalid Instruction {:08x}", instr.0);
                 break;
             }
         }