Alloc at least 1 elem in pool_t block_ptrs. (flame#560)

Details:
- Previously, the block_ptrs field of the pool_t was allowed to be
  initialized as any unsigned integer, including 0. However, a length of
  0 could be problematic given that malloc(0) is undefined and therefore
  variable across implementations. As a safety measure, we check for
  block_ptrs array lengths of 0 and, in that case, increase them to 1.
- Co-authored-by: Minh Quan Ho <[email protected]>

Change-Id: I1e885d887aaba5e73df091ef52e6c327fd6418de

frame/base/bli_pool.c

@@ -52,6 +52,11 @@ void bli_pool_init
 	// Make sure that block_ptrs_len is at least num_blocks.
 	block_ptrs_len = bli_max( block_ptrs_len, num_blocks );
 
+	// Handle the case where block_ptrs_len is zero, we explicitly set it to 1,
+	// to avoid any malloc() with zero size, whose behavior is not fixed, and
+	// also to prevent from falling into any further memory corruption bug.
+	block_ptrs_len = ( block_ptrs_len == 0 ) ? 1 : block_ptrs_len;
+
 	#ifdef BLIS_ENABLE_MEM_TRACING
 	printf( "bli_pool_init(): allocating block_ptrs (length %d): ",
 	        ( int )block_ptrs_len );