Bug#25505 Myisam library compiler error on Windows

myisam/mi_packrec.c:
  Combine the declaration of variable and assignment into one line
  since that is allowed befgore declaring another variable in C.

myisam/mi_packrec.c

@@ -590,8 +590,7 @@ static void fill_quick_table(uint16 *table, uint bits, uint max_bits,
 static uint copy_decode_table(uint16 *to_pos, uint offset,
 			      uint16 *decode_table)
 {
-  uint prev_offset;
-  prev_offset= offset;
+  uint prev_offset= offset;
   DBUG_ENTER("copy_decode_table");
 
   /* Descent on the left side. */