Fix DivideByZero exception when filesystem is completely full.

lfs.c

@@ -688,7 +688,7 @@ static int lfs_alloc(lfs_t *lfs, lfs_block_t *block) {
         if (lfs->lookahead.ckpoint <= 0) {
             LFS_ERROR("No more free space 0x%"PRIx32,
                     (lfs->lookahead.start + lfs->lookahead.next)
-                        % lfs->cfg->block_count);
+                        % lfs->block_count);
             return LFS_ERR_NOSPC;
         }
 

lfs.h

@@ -204,6 +204,7 @@ struct lfs_config {
     lfs_size_t block_size;
 
     // Number of erasable blocks on the device.
+    // If 0, will attempt to infer block_count from existing filesystem.
     lfs_size_t block_count;
 
     // Number of erase cycles before littlefs evicts metadata logs and moves