mtime fix

commit 735916aefbb07878c607fcea61259930f527582c
Author: Rahul Sinha <rahul.sinha@mpimet.mpg.de>
Date:   Sat Aug 2 09:21:41 2014 +0200

FIX: Bug reported in ICON. 'The function getPTStringFromMS returns
the string -P00.000S for 0'

mtime/src/mtime_timedelta.c

@@ -1766,7 +1766,7 @@ getPTStringFromMS(int64_t _ms, char* PTstr)
        /* ERROR: Conversion greater than 23:59:59:999 not supported. */
        return NULL;
      }
-   else if (_ms > 0)
+   else if (_ms >= 0)
      jd = newJulianDelta('+', 0, _ms); 
    else
      jd = newJulianDelta('-', 0, _ms);