Various bugfixes

While working on the mingw64 port, I found and squashed the following little bugs in our current codebase:

• pd/extra/fiddle~/fiddle~.c: sigfiddle_doinit(): removed bogus ! operator (backported from vanilla rev. 2c98b929)
• pd/src/import.c: import_output(): fix potentially unterminated strncpy
• externals/bassemu~/bassemu~.c: bassemu_list(): bogus assignment, changed to equality

Note that this MR is based on !514 (merged), so you can kill two birds with one stone by just merging this one and ignoring the other. :)

One of my Windows CI builds just died (read-only file system), the other hit a timeout. :( Also, the raspbian_stretch runner is apparently down. Other than that, the CI looks good, though.

Just fixed the windows runner. I'll re-run it.

Thanks, that did it. raspbian_stretch is still stuck, but as the other Linux runners are all green, I'd say that this is good to be merged.

so you can kill two birds with one stone by just merging this one and ignoring the other. :)

Too late :(

merged