fixed check interval for square root

source/texk/web2c/mplibdir/mpmathinterval.w

@@ -161,6 +161,7 @@ static int mpfi_remainder_2 (mpfi_t ROP, mpfi_t OP1, mpfi_t OP2) ;
 
 @d mpfi_negative_p(a) (mpfi_is_strictly_neg((a))>0) 
 @d mpfi_positive_p(a) (mpfi_is_strictly_pos((a))>0)
+@d mpfi_nonnegative_p(a) (mpfi_is_nonneg((a))>0)
 @d checkZero(dec)  if (mpfi_has_zero(dec) ) { // CHECK or mpfi_is_zero ?
      mpfi_set_d(dec,0.0);
    }
@@ -1679,7 +1680,7 @@ relying on |real| arithmetic or system subroutines for sines, cosines, etc.
 
 @c
 void mp_interval_square_rt (MP mp, mp_number *ret, mp_number x_orig) { /* return, x: scaled */
-  if (!mpfi_positive_p((mpfi_ptr)x_orig.data.num)) {
+  if (!mpfi_nonnegative_p((mpfi_ptr)x_orig.data.num)) {
     @<Handle square root of zero or negative argument@>;
   } else {
     mpfi_sqrt(ret->data.num, x_orig.data.num);