Provide better error message when there's no CD in the drive

Fixes #385.

Signed-off-by: JoeLametta <JoeLametta@users.noreply.github.com>

whipper/command/cd.py

@@ -94,6 +94,9 @@ class _CD(BaseCommand):
 
         utils.load_device(self.device)
         utils.unmount_device(self.device)
+        # Exit and inform the user if there's no CD in the disk drive
+        if drive.get_cdrom_drive_status(self.device):  # rc == 1 means no disc
+            raise OSError("no CD detected, please insert one and retry")
 
         # first, read the normal TOC, which is fast
         self.ittoc = self.program.getFastToc(self.runner, self.device)