refine comment

Author: MichaelChirico

src/fread.c

@@ -931,7 +931,7 @@ static void parse_double_hexadecimal(FieldParseContext *ctx)
 
   // Important!
   // Keep in mind that only ch[0] is guaranteed to be mapped.
-  // Rearanging these checks will lead to segfaults in rare cases.
+  // Rearranging these checks (e.g. to make 'subnormal' const) will lead to segfaults in rare cases.
   if (ch[0] == '0' && (ch[1] == 'x' || ch[1] == 'X') &&
       (ch[2] == '1' || (subnormal = (ch[2] == '0'))) && ch[3] == '.') {
     ch += 4;