Prevent segfault on ARM

CHANGELOG.md

@@ -1,5 +1,11 @@
 # Changelog
 
+## TBD - TBD
+
+Bug Fixes
+
+- Prevent GC segmentation fault on ARM platforms (Raspberry Pi 2).
+
 ## 0.9.3 - October 1, 2018
 
 Features

gc.c

@@ -1985,9 +1985,11 @@ fprintf(stdout, "done tracing, cooperator is clearing full bits\n");
           unswept++;
         }
       }
+      if (h_head) {
         h_head->num_unswept_children = unswept;
         //printf("set num_unswept_children = %d computed = %d\n", h_head->num_unswept_children, gc_num_unswept_heaps(h_head));
       }
+    }
 
     // At least for now, let the main thread help clean up any terminated threads
     if (thd == primordial_thread) {