Check cartridge ram size upon load

src/cartridge.rs

@@ -84,6 +84,9 @@ impl Cartridge {
         if let &Some(ref filename) = save_file {
             let data = super::read_file(&filename);
             if let Ok(data) = data {
+                if data.len() != size {
+                    panic!("Ram size does not match");
+                }
                 data
             } else {
                 // Generate empty buffer