Merge branch 'fix_negative_start_lat' into release-v4.2 (PR #145)

This merge fixes an issue in scaling negative starting latitudes in GRIB2
datasets on a Gaussian grid.

Prior to the changes in this merge, the code in rd_grib2.F compared the starting
latitude for a field on a Gaussian grid with the scaling factor, and if
the starting latitude was larger than the scaling factor, the starting latitude
was scaled. However, this fails when the starting latitude is negative, in which
case no scaling is applied, and downstream code fails due to an invalid starting
latitude in the resulting intermediate file.

The fix in this merge is to simply compare the magnitude of the starting
latitude with the scaling factor, and if the former exceeds the latter, then
scaling of the starting latitude is performed.

Thanks to Linda Maoyi for identifying the issue addressed in this merge.

This merge fixes issue #142 .

* fix_negative_start_lat:
  Fix scaling of negative starting latitude for Gaussian grids in g2print
  Fix scaling of starting latitude in GRIB2 datasets on a Gaussian grid

ungrib/src/g2print.F

@@ -562,7 +562,7 @@ SUBROUTINE r_grib2(junit, gribflnm, hdate,  &
               endif
 
               ! Scale lat/lon values to 0-180, default range is 1e6.
-              if (map%lat1.ge.scale_factor) then 
+              if (abs(map%lat1).ge.scale_factor) then 
                  map%lat1 = map%lat1/scale_factor
               endif
               if (map%lon1.ge.scale_factor) then 

ungrib/src/rd_grib2.F

@@ -492,7 +492,7 @@ SUBROUTINE rd_grib2(junit, gribflnm, hdate,
               endif
 
               ! Scale lat/lon values to 0-180, default range is 1e6.
-              if (map%lat1.ge.scale_factor) then 
+              if (abs(map%lat1).ge.scale_factor) then
                  map%lat1 = map%lat1/scale_factor
               endif
               if (map%lon1.ge.scale_factor) then