ast: Correct masking of regions that have no overlap with supplied array

If masking the outside of an array, and the regionb does not overlap the
supplied array, then the whole array should be masked. Previously, the
array was left unchanged.

libraries/ast/region.c

@@ -217,6 +217,8 @@ f     - AST_SHOWMESH: Display a mesh of points on the surface of a Region
 *        Guard against division by zero in RegBase Grid if "ipr" is zero.
 *     7-NOV-2013 (DSB):
 *        Added method astGetRegionFrameSet.
+*     3-FEB-2014 (DSB):
+*        Fix bug masking regions that have no overlap with the supplied array.
 *class--
 
 *  Implementation Notes:
@@ -5665,12 +5667,21 @@ static int Mask##X( AstRegion *this, AstMapping *map, int inside, int ndim, \
             ubndg[ idim ] = ubnd[ idim ]; \
          } \
          npix *= ( ubnd[ idim ] - lbnd[ idim ] + 1 ); \
-         npixg *= ( ubndg[ idim ] - lbndg[ idim ] + 1 ); \
-         if( npixg <= 0 ) break; \
+         if( npixg >= 0 ) npixg *= ( ubndg[ idim ] - lbndg[ idim ] + 1 ); \
       } \
 \
+/* If the bounding box is null, fill the mask with the supplied value if \
+   we assigning the value to the outside of the region (do the opposite if \
+   the Region has been negated). */ \
+      if( npixg <= 0 && astOK ) { \
+         if( ( inside != 0 ) == ( astGetNegated( used_region ) != 0 ) ) { \
+            c = in; \
+            for( ipix = 0; ipix < npix; ipix++ ) *(c++) = val; \
+            result = npix; \
+         } \
+\
 /* If the bounding box is null, return without action. */ \
-      if( npixg > 0 && astOK ) { \
+      } else if( npixg > 0 && astOK ) { \
 \
 /* All points outside this box are either all inside, or all outside, the \
    Region. So we can speed up processing by setting all the points which are \