vm-nuke-altrnative-text/html malfunctions

[Uday Reddy]

Trying to do M-0 vm-nuke-alternative-text/html on an entire folder gives rise the following issues/problems:

- It prints silly messages like "No text/html parts found" or "1 text/html part deleted", repeatedly.

- It damages the threads database, which can be found by turning on vm-thread-debug. ("Spurious message" etc.)

- Finally, it says "Problem detected with the threads database; try vm-fix-my-summary"

- It also gives an error message "Symbol's function definition is void: vm-fetch-nil-message-size".

[Uday Reddy (reddyuday)]

The last problem (which is pretty fatal) happens because

- the byte-count field has become nil for some message, which should only happen if the message is external.
- it tries to fetch message from the external source which is "nil".