Fix get_maps failure when GC_repeat_read returns zero

(a cherry-pick of commit 9ddc5ceb4 from 'release-8_2')

* os_dep.c [NEED_PROC_MAPS] (GC_get_maps): Do not return 0 from the
function if GC_repeat_read returns 0 unless maps_size is 0.

1 files changed, 1 insertions, 1 deletions

diff --git a/os_dep.c b/os_dep.c
index 86c499ae..ba77cf7b 100644
--- a/os_dep.c
+++ b/os_dep.c
@@ -225,7 +225,7 @@ GC_INNER char * GC_get_maps(void)
                 maps_size += result;
             } while ((size_t)result == maps_buf_sz-1);
             close(f);
-            if (result <= 0)
+            if (result < 0 || 0 == maps_size)
               return 0;
 #           ifdef THREADS
               if (maps_size > old_maps_size) {