do_readline: create new mortal with less branching

Author: richardleach

pp_hot.c

@@ -4183,7 +4183,8 @@ Perl_do_readline(pTHX)
     }
     else {
         /* XXX on RC builds, push on stack rather than mortalize ? */
-        sv = sv_2mortal(newSV(80));
+        sv = newSV_type_mortal(SVt_PV);
+        sv_grow_fresh(sv, 81);
         offset = 0;
     }
 
@@ -4310,7 +4311,8 @@ Perl_do_readline(pTHX)
                 SvPV_shrink_to_cur(sv);
             }
             /* XXX on RC builds, push on stack rather than mortalize ? */
-            sv = sv_2mortal(newSV(80));
+            sv = newSV_type_mortal(SVt_PV);
+            sv_grow_fresh(sv, 81);
             continue;
         }