[tgaxis] add epsilon for ticks counts

When caclucating number of extra ticks
which need to be placed on left or right side of axis
add `epsilon` to avoid possible rounding problems.

Ensure that minor tick on very begin or very end of axis range is painted

Author: linev

graf2d/graf/src/TGaxis.cxx

@@ -1730,7 +1730,7 @@ void TGaxis::PaintAxis(Double_t xmin, Double_t ymin, Double_t xmax, Double_t yma
 
          if (fFunction) axis_length0 = binLow-wmin;
          if ((!optionNoopt || optionInt) && axis_length0) {
-            nticks0 = Int_t(axis_length0/dxtick);
+            nticks0 = Int_t(axis_length0/dxtick + epsilon);
             if (nticks0 > 1000) nticks0 = 1000;
             xtick0 -= dxtick; // skip first major tick which already was drawn
             for (k=1; k<=nticks0; k++) {
@@ -1775,7 +1775,7 @@ void TGaxis::PaintAxis(Double_t xmin, Double_t ymin, Double_t xmax, Double_t yma
 
          if (fFunction) axis_length1 = wmax-binHigh;
          if ((!optionNoopt || optionInt) && axis_length1) {
-            nticks1 = int(axis_length1/dxtick);
+            nticks1 = int(axis_length1/dxtick + epsilon);
             if (nticks1 > 1000) nticks1 = 1000;
             xtick1 += dxtick; // skip last major tick which was already drawn
             for (k=1; k<=nticks1; k++) {