Sticky MOUNT D64 and Short Name Issues

[johnwayner]

Test Environment (required)

• Platform: MEGA65R3
• ROM Release: 920411+ (development pre-release git hash: 158991d)
• Core Commit: 9AF7EFA
• HICKUP.M65 which includes this fix: HYPPO: Add freeze region for the rest of FDD3000 mega65-core#869

Describe the bug
The feature that remounts the previously mounted disk image on a reset fails in two cases:

• when the disk image name is short: A.D81, T.D64, etc.
• when the image is a D64

To Reproduce
Steps to reproduce the behavior:

1. MOUNT A.D81 (or any D64)
2. reset machine using side button
3. DIR (returns drive not ready)

Expected behavior
The previously mounted image is properly remounted so that the DIR returns a directory listing.

Additional context
I have fixes for both of these. The short name is an off-by-one error when checking for a too-short name. The second is due to the extension of the image name always being overwritten with .D81 even though the entire name is saved.

Adjacent Issue?
The ROM always remounts the most recently mounted image -- even if it was not mounted at the time of reset. This feels wrong to me, but perhaps it should be a separate issue.

[dansanderson]

We want Hyppo to own sticky mounting in the future. I don't know how close we are to implementing it but we've mostly agreed it's the right thing. #192