fixes memory issue that occurs with grids are written out, which contain cells the have no corners

src/core/basic_grid.c

@@ -804,20 +804,27 @@ void yac_basic_grid_to_file_parallel(
 
   // fill send buffer
   for (size_t i = 0, offset = 0; i < grid->data.num_cells; ++i) {
-    int j;
-    for (j = 0; j < grid->data.num_vertices_per_cell[i]; ++j) {
-      XYZtoLL(
-        grid->data.vertex_coordinates[
-          grid->data.cell_to_vertex[
-            grid->data.cell_to_vertex_offsets[i] + j]],
-        sendbuffer_dble + offset + 2 * j + 0,
-        sendbuffer_dble + offset + 2 * j + 1);
-      sendbuffer_dble[offset + 2 * j + 0] /= YAC_RAD;
-      sendbuffer_dble[offset + 2 * j + 1] /= YAC_RAD;
-    }
-    for (; j < max_num_vertices_per_cell; ++j) {
-      sendbuffer_dble[offset + 2 * j + 0] = sendbuffer_dble[offset + 0];
-      sendbuffer_dble[offset + 2 * j + 1] = sendbuffer_dble[offset + 1];
+    if (grid->data.num_vertices_per_cell[i] > 0) {
+      int j;
+      for (j = 0; j < grid->data.num_vertices_per_cell[i]; ++j) {
+        XYZtoLL(
+          grid->data.vertex_coordinates[
+            grid->data.cell_to_vertex[
+              grid->data.cell_to_vertex_offsets[i] + j]],
+          sendbuffer_dble + offset + 2 * j + 0,
+          sendbuffer_dble + offset + 2 * j + 1);
+        sendbuffer_dble[offset + 2 * j + 0] /= YAC_RAD;
+        sendbuffer_dble[offset + 2 * j + 1] /= YAC_RAD;
+      }
+      for (; j < max_num_vertices_per_cell; ++j) {
+        sendbuffer_dble[offset + 2 * j + 0] = sendbuffer_dble[offset + 0];
+        sendbuffer_dble[offset + 2 * j + 1] = sendbuffer_dble[offset + 1];
+      }
+    } else {
+      for (int j = 0; j < max_num_vertices_per_cell; ++j) {
+        sendbuffer_dble[offset + 2 * j + 0] = DBL_MAX;
+        sendbuffer_dble[offset + 2 * j + 1] = DBL_MAX;
+      }
     }
     offset += 2 * (size_t)max_num_vertices_per_cell;