Fix build warnings about missing field initializer

[rbuj]

test_metar.c:24:9: warning: missing field 'short_name' initializer [-Wmissing-field-initializers]
        { NULL }
               ^
--
test_sun_moon.c:30:9: warning: missing field 'short_name' initializer [-Wmissing-field-initializers]
        { NULL }
               ^

[mbkma]

LGTM, builds fine

[lukefromdc]

These build with no warnings w my default build options. The two test files changed test_metar and test_sun_moon seem to work fine, though I don't really know how to test them right. test_sun_moon definately gave a chart of valid looking results when fed a valid latitude and longitude however

[lukefromdc]

We really should get a 1.27.0 release of this out BTW