Fix bug in recent allocate_string_data patch

Reported by Glenn Morris in:
https://lists.gnu.org/r/emacs-devel/2020-01/msg00098.html
* src/alloc.c (allocate_string_data): If the string is small and
there is not enough room in the current block, clear the string if
CLEARIT.

1 files changed, 18 insertions, 17 deletions

diff --git a/src/alloc.c b/src/alloc.c
index d6d456a8fc0..7eb37bb12da 100644
--- a/src/alloc.c
+++ b/src/alloc.c
@@ -1831,26 +1831,27 @@ allocate_string_data (struct Lisp_String *s,
       b->next_free = data;
       large_sblocks = b;
     }
-  else if (current_sblock == NULL
-           || (((char *) current_sblock + SBLOCK_SIZE
-                - (char *) current_sblock->next_free)
-               < (needed + GC_STRING_EXTRA)))
-    {
-      /* Not enough room in the current sblock.  */
-      b = lisp_malloc (SBLOCK_SIZE, false, MEM_TYPE_NON_LISP);
-      data = b->data;
-      b->next = NULL;
-      b->next_free = data;
-
-      if (current_sblock)
-        current_sblock->next = b;
-      else
-        oldest_sblock = b;
-      current_sblock = b;
-    }
   else
     {
       b = current_sblock;
+
+      if (b == NULL
+          || (SBLOCK_SIZE - GC_STRING_EXTRA
+              < (char *) b->next_free - (char *) b + needed))
+        {
+          /* Not enough room in the current sblock.  */
+          b = lisp_malloc (SBLOCK_SIZE, false, MEM_TYPE_NON_LISP);
+          data = b->data;
+          b->next = NULL;
+          b->next_free = data;
+
+          if (current_sblock)
+            current_sblock->next = b;
+          else
+            oldest_sblock = b;
+          current_sblock = b;
+        }
+
       data = b->next_free;
       if (clearit)
         memset (SDATA_DATA (data), 0, nbytes);