Valenar crash: bad report interval when a faction has no units.

src/reports.c

@@ -1367,6 +1367,9 @@ void reorder_units(region * r)
 
 static region *lastregion(faction * f)
 {
+    if (!f->units) {
+        return NULL;
+    }
     return f->last ? f->last->next : NULL;
 }
 
@@ -1418,6 +1421,7 @@ void prepare_report(report_context *ctx, faction *f)
     ctx->addresses = NULL;
     ctx->userdata = NULL;
     /* [first,last) interval of regions with a unit in it: */
+    if (f->units) {
         ctx->first = firstregion(f);
         ctx->last = lastregion(f);
 
@@ -1457,6 +1461,7 @@ void prepare_report(report_context *ctx, faction *f)
                 travelthru_map(r, cb_add_seen, f);
             }
         }
+    }
     /* [fast,last) interval of seen regions (with lighthouses and travel)
      * TODO: what about neighbours? when are they included? do we need
      * them outside of the CR? */