r.viewshed: initialize struct member before using struct (#4232)

* r.viewshed: initialize struct member before using struct

This was reported by cppcheck tool. Technically, we are not using
the member in the struct variable in any of the subsequent
functions, but it's a good practice to initialize all the struct
members whenever possible.

Signed-off-by: Mohan Yelugoti <ymdatta.work@gmail.com>

* Use right literal while initializing angle

Signed-off-by: Mohan Yelugoti <ymdatta.work@gmail.com>

---------

Signed-off-by: Mohan Yelugoti <ymdatta.work@gmail.com>

raster/r.viewshed/viewshed.cpp

@@ -261,6 +261,7 @@ MemoryVisibilityGrid *viewshed_in_memory(char *inputfname, GridHeader *hd,
         e.elev[0] = data[0][i];
         e.elev[1] = data[1][i];
         e.elev[2] = data[2][i];
+        e.angle = -1.0;
 
         if (!is_nodata(visgrid->grid->hd, data[1][i]) &&
             !is_point_outside_max_dist(*vp, *hd, sn.row, sn.col,
@@ -499,6 +500,7 @@ IOVisibilityGrid *viewshed_external(char *inputfname, GridHeader *hd,
         e.elev[0] = data[0][i];
         e.elev[1] = data[1][i];
         e.elev[2] = data[2][i];
+        e.angle = -1.0;
         if (!is_nodata(visgrid->hd, data[1][i]) &&
             !is_point_outside_max_dist(*vp, *hd, sn.row, sn.col,
                                        viewOptions.maxDist)) {