garmin_txt: Fix MSVC crash with timestamps lt zero.

diff --git a/gpsbabel/garmin_txt.c b/gpsbabel/garmin_txt.c
index a31e118154d623fe3463a52a0eb7365d4ecef67d..a8122ca1ce89474ca506131d9ed8ab6116c74bf0 100644 (file)
--- a/gpsbabel/garmin_txt.c
+++ b/gpsbabel/garmin_txt.c
@@ -358,6 +358,10 @@ print_date_and_time(const time_t time, const int time_only)
        struct tm tm;
        char tbuf[32];
        
+       if (time < 0) {
+               gbfprintf(fout, "\t");
+               return;
+       }
        if (time_only) {
                tm = *gmtime(&time);
                snprintf(tbuf, sizeof(tbuf), "%d:%02d:%02d", tm.tm_hour, tm.tm_min, tm.tm_sec);