gpsutils: Fix unix_to_iso8601 NaN case.

Since the return type of unix_to_iso8601 is non-const, it's illegal
to return a pointer to a string constant.  Some compilers report
a warning for this.  The fix is to copy the string to the provided
buffer.

It would be nice to add a test case for this, but there doesn't seem
to be any portable way to get NaN as a constant in C.

TESTED:
The warning is gone, and the tests still pass.

1 files changed, 1 insertions, 1 deletions

diff --git a/gpsutils.c b/gpsutils.c
index 3ae49e4d..d4a2a5fe 100644
--- a/gpsutils.c
+++ b/gpsutils.c
@@ -532,7 +532,7 @@ char *unix_to_iso8601(timestamp_t fixtime, char isotime[], size_t len)
     char fractstr[10];
 
     if (!isfinite(fixtime)) {
-        return "NaN";
+        return strncpy(isotime, "NaN", len);
     }
     fractional = modf(fixtime, &integral);
     /* snprintf rounding of %3f can get ugly, so pre-round */