Emulator: Add error message when reading unloaded cartridge header

src/emu.cpp

@@ -12,6 +12,7 @@
 
 #include "cpu.h"
 #include "emu.h"
+#include "ruc/format/log.h"
 #include "ruc/format/print.h"
 #include "ruc/meta/assert.h"
 
@@ -82,6 +83,11 @@ uint32_t Emu::readMemory(uint32_t address) const
 		}
 	}
 
+	// When trying to access the cartridge header
+	if (address >= 0x100 && address <= 0x14f) {
+		ruc::error("No cartridge loaded!");
+	}
+
 	VERIFY_NOT_REACHED();
 	return 0;
 }