[gpad] do not use floating type as loop counter

see https://stackoverflow.com/questions/16595668/is-there-any-risk-of-using-float-variables-as-loop-counters-and-their-fractional

Author: ferdymercury

graf2d/gpad/src/TPad.cxx

@@ -4178,7 +4178,7 @@ void TPad::PaintHatches(Double_t dy, Double_t angle,
                         Int_t nn, Double_t *xx, Double_t *yy)
 {
    Int_t i, i1, i2, nbi, m, inv;
-   Double_t ratiox, ratioy, ymin, ymax, yrot, ycur;
+   Double_t ratiox, ratioy, ymin, ymax, yrot;
    const Double_t angr  = TMath::Pi()*(180.-angle)/180.;
    const Double_t epsil = 0.0001;
    const Int_t maxnbi = 100;
@@ -4220,8 +4220,10 @@ void TPad::PaintHatches(Double_t dy, Double_t angle,
       if (yrot < ymin) ymin = yrot;
    }
    ymax = (Double_t)((Int_t)(ymax/dy))*dy;
-
-   for (ycur=ymax; ycur>=ymin; ycur=ycur-dy) {
+   
+   const Int_t nYsteps = static_cast<Int_t>((ymax - ymin)/dy) + 1;
+   for (Int_t icur = 0; icur < nYsteps; ++icur) {
+      const Double_t ycur = ymax - icur * dy;
       nbi = 0;
       for (i=2; i<=nn+1; i++) {
          i2 = i;