MDEV-8395: InnoDB: Assertion failure in file fil0pagecompress.cc line 539 (SIGFPE)

File block size might be 0 and used on modulo operator. Make sure that
file block size is initialized to 512.

storage/innobase/fil/fil0pagecompress.cc

@@ -355,12 +355,16 @@ fil_compress_page(
 
 	write_size+=header_len;
 
+	if (block_size <= 0) {
+		block_size = 512;
+	}
+
+	ut_ad(write_size > 0 && block_size > 0);
+
 	/* Actual write needs to be alligned on block size */
 	if (write_size % block_size) {
 		size_t tmp = write_size;
-#ifdef UNIV_DEBUG
-		ut_a(block_size > 0);
-#endif
+
 		write_size =  (size_t)ut_uint64_align_up((ib_uint64_t)write_size, block_size);
 #ifdef UNIV_DEBUG
 		ut_a(write_size > 0 && ((write_size % block_size) == 0));

storage/xtradb/fil/fil0pagecompress.cc

@@ -355,12 +355,16 @@ fil_compress_page(
 
 	write_size+=header_len;
 
+	if (block_size <= 0) {
+		block_size = 512;
+	}
+
+	ut_ad(write_size > 0 && block_size > 0);
+
 	/* Actual write needs to be alligned on block size */
 	if (write_size % block_size) {
 		size_t tmp = write_size;
-#ifdef UNIV_DEBUG
-		ut_a(block_size > 0);
-#endif
+
 		write_size =  (size_t)ut_uint64_align_up((ib_uint64_t)write_size, block_size);
 #ifdef UNIV_DEBUG
 		ut_a(write_size > 0 && ((write_size % block_size) == 0));