Fix crash on download from Navin/ZNEX miniHomer

[kgraefe]

This adds the options gps-utc-offset and gps-week-rollover to the
miniHomer driver. By adding them solely to the skytraq driver they were
initialized with nullptr for the miniHomer ultimately leading to a
crash.

This fixes #351.

[tsteven4]

Nice.

Did our current skytraq test fail on your architecture? Our basic test is invoked with the testo script. It reads scripts in the testo.d directory, e.g. skytraq.test. I would have hoped the test using skytraq-miniHomer2_8.bin would have been capable of finding this bug, at least if run on ARM.
Without your fix and using your architecture please try "./testo skytraq". Then try it with your fix on your architecture.

If the test fails w/o the fix, and passes with it, then we can blame our finite test environment (various flavors of ubuntu + windows + macos). But if the test doesn't fail w/o the fix, then it would be desirable to enhance the test.

[kgraefe]

The test works well without the patch, but from what I see that's because it by design uses arglist_t skytraq_fargs[] instead of arglist_t miniHomer_args[] and that already had both options.

I don't see an easy way to test for that particular issue.

[tsteven4]

Either
char* p = nullptr; int i = atoi(p);
or
char* p = nullptr; int i = (int) strtol(p, (char **)NULL, 10);
will segfault on Ubuntu bionic. This has nothing to do with ARM and everything to do with de-referencing a null pointer.

ubsan can find these if we execute the code:
test.cc:7:22: runtime error: null pointer passed as argument 1, which is declared to never be null
/usr/include/stdlib.h:178:14: note: nonnull attribute specified here
UndefinedBehaviorSanitizer:DEADLYSIGNAL
==13709==ERROR: UndefinedBehaviorSanitizer: SEGV on unknown address 0x000000000000 (pc 0x7f7a5da1b1b0 bp 0x000000000000 sp 0x7ffee04dcde0 T13709)

but, as @kgraefe points out, we only execute the problematic code when we actually have the serial device connected.

I don't see an easy way to improve the test. One might consider:

• Some formats use gbser_is_serial instead of duplicating the argument vectors, e.g. magproto.

• converting argument passing to use QStrings.

but these are longer term projects.

[tsteven4]

I will merge this as it seems clearly to be an improvement, but I am unsatisfied with the testing methodology that leaves us open to creating these kinds of errors between skytraq and minihomer developers.