Fix iterations through arenas

src/libImaging/Imaging.h

@@ -195,13 +195,13 @@ typedef struct ImagingMemoryArena {
  * will allocate a set of arenas and associated them with threads one at a time.
  */
 #define IMAGING_ARENAS_COUNT 8
-extern struct ImagingMemoryArena ImagingArenas[IMAGING_ARENAS_COUNT];
+extern struct ImagingMemoryArena ImagingArenas[IMAGING_ARENAS_COUNT+1];
 
 /* Provide a macro that loops through each arena that has been
  * statically-allocated. This is necessary to properly handle stats.
  */
 #define IMAGING_ARENAS_FOREACH(arena) \
-    for ((arena) = &ImagingArenas[0]; arena->block_size; ++(arena))
+    for ((arena) = &ImagingArenas[0]; (arena)->alignment >= 0; ++(arena))
 #else
 /* In this case we either have the GIL or do not have thread-local storage, in
  * which case we will only allocate a single arena.

src/libImaging/Storage.c

@@ -273,7 +273,7 @@ static uint64_t ImagingArenaIndex = 0;
 static IMAGING_TLS uint64_t ImagingArenaThreadIndex = UINT64_MAX;
 
 /* These are the statically-allocated arenas. */
-struct ImagingMemoryArena ImagingArenas[IMAGING_ARENAS_COUNT] = {
+struct ImagingMemoryArena ImagingArenas[IMAGING_ARENAS_COUNT+1] = {
     {1, IMAGING_ARENA_BLOCK_SIZE, 0, 0, NULL, 0, 0, 0, 0, 0, 0, {0}},
     {1, IMAGING_ARENA_BLOCK_SIZE, 0, 0, NULL, 0, 0, 0, 0, 0, 1, {0}},
     {1, IMAGING_ARENA_BLOCK_SIZE, 0, 0, NULL, 0, 0, 0, 0, 0, 2, {0}},
@@ -282,7 +282,7 @@ struct ImagingMemoryArena ImagingArenas[IMAGING_ARENAS_COUNT] = {
     {1, IMAGING_ARENA_BLOCK_SIZE, 0, 0, NULL, 0, 0, 0, 0, 0, 5, {0}},
     {1, IMAGING_ARENA_BLOCK_SIZE, 0, 0, NULL, 0, 0, 0, 0, 0, 6, {0}},
     {1, IMAGING_ARENA_BLOCK_SIZE, 0, 0, NULL, 0, 0, 0, 0, 0, 7, {0}},
-    {0}
+    {-1},
 };
 
 /* Get a pointer to the correct arena for this context. In this case where we