Fix off-by-one error introduced in r77483.  I have a test for this, but it currently fails due to a different dtoa.c bug;  I'll add the test once that bug is fixed.
diff --git a/Python/dtoa.c b/Python/dtoa.c
index 8389eb2..59833a0 100644
--- a/Python/dtoa.c
+++ b/Python/dtoa.c
@@ -1303,7 +1303,7 @@
         if (dd)
             goto ret;
         if (!b->x[0] && b->wds == 1) {
-            if (i < nd)
+            if (i < nd - 1)
                 dd = 1;
             goto ret;
         }
@@ -1319,7 +1319,7 @@
         if (dd)
             goto ret;
         if (!b->x[0] && b->wds == 1) {
-            if (i < nd)
+            if (i < nd - 1)
                 dd = 1;
             goto ret;
         }